Just got it, "upgraded" from XP pro X86.  I use to get 30-50 FPS in oblivion w/ all settings maxed out with HDR and 2xAA enabled.  

Now in vista x64 my frames drop to the teens sometimes while outside.  Do I need to install direct X 9 or something?

Or is it because I just don't have enough memory.  Here is what I am running:

*edit* yeah, I have the latest driver's from Nvidia, I did not even bother w/ the ones on the disk when I installed drivers.  

Guess I should have mentioned my Res, 1920x1080 (30 FPS does not sound so offal now does it).  The FPS dropping to 15 is what pisses me off though.  That never happened in XP unless there were a lot of enemies on screen.  

Oh, and this is a gaming PC exclusively so I never have anything else running.  

I will take this all into account, thats guys.  

E8400
EVGA 8800GT superclocked edition
2 gigs pc 800 ram dual channel mode
Seagate 7200.8 (yeah I know its old)

Turn off AA. Oblivion was not initially designed to use AA and HDR together, at least not with GeForce cards. Driver updates eventually allowed it to be forced but drivers are still not fully matured in Vista. This doesn't guarantee you'll get better performance but it's the first thing I would try. I also play Oblivion with the system in my sig and I easily get 40+ fps even in the more intense enviroments, but usually 50-60 (with Vsync on, with it off I'll got 200+ in doors sometimes).

one word, "VISTA"

Incredibly helpful Flakes. One of the biggest issues of using Vista is the fact that half of the responses you'll get when looking for help will be "Vista Suckz!". While I'm not entirely sure why you would have switched if XP wasn't giving you an issue, there's no reason why you should be getting that low of frame rates on Oblivion with the hardware you have. Besides my above advice, have you fully updated everything? If you just installed Vista and haven't run every update and went out and got every updated driver chances are you may have some Nov. 2006 dated drivers or files that could be holding you back. Also try scaling back the settings to see when you start to get more reasonable frame rates. Even if that's not how you want to play the game it will give you an idea of how far off you are. If turning down one setting makes a noticeable difference (like turning off AA) you may not be far off and just need a little tweaking. If you really have to dial it down then there is most likely bigger issues.

Try forcing DX9 only? if you can in oblivion.

Oblivion doesn't use any DX10 features so it is automatically DX9.

theres no easy way to explain this
but here 3 reasons why you may have the sudden slowness
sry for the image quality, the forum software is being dumb and resizing the images by a few pixels making it hard to read, just click to zoom

what is bringing about these higher requirements, all they really did was add direct x 10, some eye candy and a side bar what is causing the insane requirements for a OS, (seems to be poor programming. in terms of functionality and features, nothing was really added to the os beside eye candy. the problem is that is is so inefficient that it runs slower. (based on what was added to the os, the requirements don't add up)

you may have a pretty good gaming pc but that  doesnt stop vista from being inefficient.

you can have a 1001 horsepower car but if you add a trailer (aka vista) onto the back of it, it wont be breaking any speed records anytime soon, it will still go highway speeds but  who spends over a million dollars to go highway speeds ?

PS the op is not interested in turning down the settings, if he was, he wouldn't have posted this topic. he mainly wants to know why it ran smooth in xp but slow in vista.

Razor did you even look at those minimum specs? He's so far beyond it that it shouldn't even matter. Also those charts are somewhat misleading. '95-XP = 6 years, XP-Vista - 6 years. Also XP mins are 2001 mins, not 2008 mins with years of updates. Do a little research and you'll see that with the specs he has Vista should not account for more than a 10% decrease. What he is experiancing is far beyond that. As with any time you install a fresh copy of ANY OS, or really any software some configuration my be required.  
I'm not telling him to lower settings so that he'll get better FPS and live with it. What I'm saying is to lower settings until you get a good FPS then work your way back up slowly while tweaking settings/the system to see where you are losing performance.
BTW I'll take Vista with 800mhz/15GB/512MB over XP with 233/1.5/64.

I also just want to throw it out there that 30-50fps in Oblivion on XP with those specs is a little low to.
 
Here's what you should expect using similar specs to what you have (8800GTX is probably the closest match)
http://www.firingsquad.com/hardwar [...] /page7.asp

theres no such thing as  higher requirements not mattering,  get a car that has twice the horse poerr of your current car, then get a hitch and attach your old car to the new one and tow it, tell me how your new car seems to perform

he can have 4 trillion GHZ gaming PC and vista will still benchmark lower on it than with xp.

look at people who do racing with their cars.

even though they get better engines and tweak them for max speed, they still do weight reduction mods to their car  because  you cant say that the engine is so powerful that the weight wont matter

generally with a OS you want to os to use at little as possible so there will be more left over for actual work

if you get paid 170 billion a year because you quadrupled your oil prices. i bet you would still get pissed off if i stole $5 from you  

just because computers are faster, doesn't mean they need to make the os exponentially harder to run while adding only a few tiny things that have nothing  to do with productivity

if cars and planes followed the windows vista method, cars would weigh over 30 tons  and planes would weigh more than an apartment building

but instead, cars today  are much more powerful and weigh much less than cars from 60 years ago

look at professional programs like MAYA   requirements can actually be lower than previous versions, each new version of maya benchmarks higher than older versions because they were able to understand what upgrade really means. in the professional world, time is money. no one wants to loose money because the programmers decided to add meaningless eye candy to the UI. photoshop cs3 is faster than photoshop CS2

and if you look at the upcomming CS4, it will be what seems to be up to 1000 times faster  because it will be more efficient and they will be using the nvidia CUDA technology

vista has had a lot of poor drivers but most major companies have  got their act together but still vista has lower gaming performance

100% sure it is drivers as purplerat already identified (the Nvidia x64 drivers that shipped with Vista were fairly horrible!). Just head over to www.nvidia.com, slap on the latest driver and all should be sweet. Probably worth ensuring you have Vista SP1 as well as there are a few tweaks to file / network performance, but these wont make much difference in Oblivion.
 
I've been running Vista x64 since it first came out, and after a few teething issues it has been absolutely rock solid and performs well. Vista makes much better use of modern hardware (particularly machines with lots of RAM, contrary to some common misconceptions) although gaming is lagging slightly behind XP. There are also a lot of technical improvements in Vista to make it more manageble, stable and secure. And, no, I don't work for Microsoft!
 
There, first post on this forum after being a regular visitor to this site since around 2001. I'll go to bed before the flames start!
 

Razor, I know how fond you are of your off the wall nonsense analogies, but PCs are not cars. And  yes when it comes to PCs there is a point where hardware will surpass the difference between two OSs or any two versions of software for any practical purpose, and many times improvements in software will allow for better performance of hardware (ie. 16bit ->32bit ->64bit, single threaded -> multi-threaded).  
Anyways I'm not going to get into a Vista VS XP debate. It is clear to anybody with half a brain about the differences between Vista and XP that the amount of performance loss the OP describes based on the hardware and software he is using is not due to the difference in OSs. Both based on the link I provided as a reference and my own experience with a very similar system before I upgraded (actually a lesser system) I know that fps in the teens on Oblivion is too low for his specs regardless. So I’m trying to offer real help so that he can enjoy his game the way he wants without having to dump an OS which I’m sure wasn’t cheap. If you have any better suggestions - rather than just flinging rhetoric like a monkey does it’s feces - please feel free to chime in.

his fps are defenantly too low but if he gets all latest drivers and still has some performance problems then it is the os mostly
 
 
also you brought up going from 16 bit to 32 bit.  that was  a welcome change because it allowed for more performance, but vista did not do anything like that, all they really did was add more eye candy and a few other features that do nothing in terms of productivity.
 
I will only call a new OS an upgrade when it actually improves speed and performance (and time shifting doesn't count )
 
PS even the latest 64 bit drivers have problems with some games, (for example of a  game that is painful to run 64 bit, second life.  bad drivers + bad game engine = hell )
 
so he may get some improvement by getting the latest ones but theres still a chance that he wont get the best performance he can get from from a game running in vista  
 
PS every new windows release except vista added something new in terms of speed and performance.
 
(most newer versions of windows, increased max supported memory, added support for multiple cores, and added new file systems which allowed for support for larger filesizes and other things that improved productivity, vista did none of this, and don't say it is safer because if that was true, I wouldn't be making twice as much money than i did before vista came out, with all of the people having problems with vista  (mainly spyware  and trojans if there is any added security, it is so small that nothing can detect it  )
 
and crazy analogies are fun lol

OK Razor, go right ahead and keep arguing Vista VS XP by yourself. Enjoy! But the question was about game performance in a particular game, not about what OS is better. The truth is that 50% performance loss is not acceptable and Vista is not the excuse.  
Now back to the OPs question. Another driver related issue could be reflected in whether or not you are using Vsync and what happens when you turn it on or off?

Turn off AA is a good bet since you have to force it in drivers, plus Oblivion doesn't need it, IMO.  I get some performance drop in Vista compared to XP, but I only notice it in Quake Wars.

I was not arguing which os was better, I was talking about vista as being demanding as ONE of the reasons why he has lag, not the only reason, just one of the reasons (basically means it can be a number of things, but thats just one of the many reasons )
 
make something thats harder to run, and it will run slower, add that with bad drivers since 64 bit is not a main focus of nvidia and you can end up with a laggy game  

Razor just amazes me with every new post.  Just some crazy German guy talking to himself off in a dark corner at the bar, while everyone else is just kind of staring at him, watching him occasionally flail his arm shouting "NO! You're wrong!"
 
How often are you wearing pants when you post, Razor?

lol

I'm not German,

But if you need i can give some crazy analogies (even though they are sometimes a little crazy, they do hold some truth, make something harder to run, then it will run slower. unless they do something major like increasing supported memory, allowing more cpu cores, better multi threading and other things that will improve performance  )

Quantum computer.  Vista hurts its performance while Vista doesn't affect performance. Oh Snap!