So I just built a new computer and here are specs..
E4300, MSI P6N (Nvidia), ATI X1900GT, and 450 FSP PSU.

The problem has happened in Oblivion, Call Of Duty 2, and Star Wars Battlefront 2. The frame rates are all high then all of a sudden they just drop to around 1 and it's unplayable for 1-5 seconds, it's REALLY annoying. I updated my motherboard drivers and the ATI catalyst drivers too, what else can be wrong??

I have 2GB's of DDR2 6400 ram (G-Skill) and here's my PSU..
http://www.newegg.com/Product/Prod [...] 6817104954
And HD..
http://www.newegg.com/Product/Prod [...] 6822145087

I just found some drivers on my motherboard's site..
http://global.msi.com.tw/index.php [...] rod_no=836
When I tried to install it, I got this message...

The software you are installing for this hardware:
X1900 Series
has not passed windows logo testing to verify its compability with windows.

Then it gives me two options: Continue Anyways or STOP Installation, and it also gives me a big disclaimer scary thing about how continuing can kill my computer. Should I just continue anyways?

All my ATi drivers have always come up with that message, so I'd say just continue.

I guess ATi release drivers that frequently and patch that many things that the drivers are obsolete before they get a chance to get them Windows Logo verified.

Those are old drivers, get the newest ones here (pick your version of vista):

32-bit Vista
64-bit Vista

did u overclock that e4300? runnin it @ 1.8 could bottleneck dont u ppl think?

naaah, the E4300 is a good pcu and will run the 1900GT just fine.

well i only said it, cos i have a e4300 and sumtimes @ 1.8 it would bottleneck runnin latest games... ;o

ive had a simular problem 2 this, they way to solve it is to lower your graphics in the ati control panel! COD2 has lots of fog which is a FPS killa tbh imo!

With the new drivers, here is what I've noticed.. Oblivion doesn't slow down as often, but when it does, its longer. In COD2, it stutters more frequently, but only for 1-2 seconds. No difference in SWBF2.

I think I should just reinstall all my ATI drivers. Where are the detfinite places I can get the newest Graphics drivers and ATI Catalst drivers. (They are two seperate drivers right?)

@Randomizer I do not have Vista, I'm running Windows XP PRO
@Rizzywho I really don't think that's the problem, I'm running at 1024 on Oblivion with all on high, AA2x and no bloom or HD and I'm getting great frame rates. Everything on max on COD2 gives me 60~ frame rates.

Sorry I will link the xp ones then. 32 bit right? Or are you using 64 bit?

EDIT: Here, bookmark this page for later use. Pick your own version of windows:

http://ati.amd.com/support/driver.html

I found my graphics card on there and installed the catalyst drivers here..
http://ati.amd.com/support/drivers/xp/radeonx-xp.html

What else am I missing?

Do you have access to another PSU, just to try at this stage? Yours should be OK, but if you have one thats not so stable as it should be under load, then that will cause problems. Personally I would go for something with a little more than what yours has.

Also if you're not playing online, just try disabling your AV and firewall. You shouldn't need to with a system of those specs, but if it makes a difference, then try reinstalling them.

No, I do not have another PSU to try on. I disconnected my cd drive and it's still doing this so maybe its not the power? Tried disabling AV and firewall too (I use AVG and Sygate), still doesn't solve anything.

Can heat be the problem here? I touched my video card after a two hour session of trying to play and going online and it was really hot. What do you guys use to monitor your heat in your CPU and stuff? I Dled a program called Everest but it cannot detect any sensors.

Yeah it's not there, the only temperature reading I see is Computer -> Sensor
It has something with right now, 34C, I think that might be the system environment temp.

What brand is your video card? Some manufacturers do not include thermal monitoring capabilities (like mine).