I am in the process of building a new system. The main use will be for gaming but i will do some some light/medium video editing on it (home movies and such). I was planning on OCing whichever CPU i bought. So should i go with the e8400 as originally planned or change to q9450? Will the 8400 be able to handle the video side of it in a reasonable manner or will it struggle. How is the 9450 with gaming? Thanks for all the help.
Here is the rest setup i have planned
 
?????Intel Core 2 Duo E8400 Wolfdale?????
Visiontek Radeon HD 4870
Western Digital Caviar SE16 WD2500AAKS 250GB
SAMSUNG 22X DVD  
OCZ Reaper HPC Edition 4GB (2 x 2GB)  
COOLER MASTER RC-690
CORSAIR CMPSU-550VX
XIGMATEK HDT-S1283 w/ Retention bracket

Both are great CPUs but it really depends on how often you upgrade.  
 
If you upgrade every 6 or 12 months then the E8400 would probably be the better buy.  If you want the system to last for a few years I would recommend the Q9450.  Both CPUs will overclock past 3Ghz and will give you plenty of performance.

What software?

If your video software will use those four cores with 4 parallel threads - - - the quad - - - though it's hard to justify the price of the q9450.

You need a scatch drive, too, for your video work.

Lookee here - - - > >
CPU scaling in games with dual & quad core processors
http://www.guru3d.com/article/cpu- [...] ocessors/1

Go with the E8400 or even better a Q6600 over the Q9450. The Guru3d article measures everything at stock speeds. Look at the FPS.  Notice even at stock speeds in many games they are already faster than the the human eye perceive a difference. You won't notice any real world difference in games between any of them once over they are clocked to 3.2-3.4ghz.  So $wise it would seem that if you wanted a quad, why spend more on a end of life platform unless you need the SSE4.

Yes I would agree with Craxbax and wisecracker.
 
A: It depends on your software (multi-threaded for 4 cores)
 
and
 
B: Does your software use SSE4 and how often do you upgrade ?
 
Some of the video editing software gets a big boost from SSE4.

I'd like to get a couple of years use out of this setup if possible. I'm not sure about which program i'm going to use just yet. I have Final Cut Pro on my PPC G5 Mac but since it isn't the newer intel chipset it won't handle the HD video my camcorder can produce.

If you have a HD camcorder and need to buy new software, I would go with a SSE4 cpu.
 
I think the Q9300 would work for you as well. You'll need all 4 cores and SSE4 to get HD encoded in a decent amount of time.
 
**edit**
 
on second thought. I would pay the extra $47 for double the cache on the 9450

Q6600 or Q9450

75% gaming    
Go E8400

Since you want the system to last, I would definitely go with the Q9450.  You will get the same speed as a dual core, and as programs become more multithreaded, you system will get faster instead of slower.
 
If not the Q9450 then maybe the cheaper Q6600, which will also overclock to >3.2Ghz

is the 9450 pretty easy to overclock? This will be my first time attemping to OC.

It's fairly easy, especially just up to 3.0-3.2.

If cost is no issue, Q9450 definitely.
 
There will be very little difference in gaming performance between an E8400 and Q9450, but the Q9450 would dominate the E8400 in video editing (provided the software takes advantage of quad cores).