Okay.. I recently upgraded to an 8800gt from my previous x1950 pro gpu, and seem to be having a little issue.  While playing Call of Duty 4, after about 15-30 minutes of gameplay my computer freezes and has issues starting back up.  With the previous x1950pro gpu i had no problem running Call of Duty 4 and I'm guessing this is related to my power supply.  I'm currently running on a Corsair 450vx and I thought that it would be ample enough to run the 8800gt? other system specs include 2gb ram, e2160 OC to 3.0, windows xp, and etc.. Heat doesnt seem to be an issue because my monitoring shows it never exceeds 65 celcius.. I would play for hours on end with the old x1950pro, and im a bit disappointed that the new 8800gt is failing in comparison even at the same texture levels.. Aside from the improbability that my psu is at fault (its practically brand new) I'm guessing I might have a defective card? It seems possible, but I wouldnt know what to look for, it can max out the graphics, run below average temps and perform awesomely, yet after the 15-30 minutes of gameplay it gives out on me and my comp freezes? Anywho, I'm stumped right now, please respond with suggestions. (p.s. how and what do I RMA if necessary?)

I think your spot on about your PSU assumtion.

Have you used a driver cleaner to get rid of all the old ATI drivers? That will probably impact your performance quite a bit.
 
Personally, I don't think it's your PSU. I've run the 8800GTS 640MB on a RAIDMAX 420W PSU w/o a problem. Check the drivers before you go out and buy a new PSU / RMA the card.

Where would I get a driver cleaner? Is this actually a possibility the drivers are an issue? I'm fairly sure I uninstalled everything and installed all the current drivers for the 8800gt.  As I said before, this is all a fairly new system (maybe 3months old) and I just recently upgraded to the 8800gt.  Prior to the upgrade, all my games were running fine, but now I cant last much longer for 30 minutes without freezing.

 
I personally wouldn't blame the PSU right off the bat. I  have a little Thermaltake Purepower 500W PSU with only 12V1 14A and 12V2 15A. I literally have pretty much the same setup(E2180 @3Ghz, 8800GT @ 700/1990,4x1GB RAM, 1HDD) and it runs fine. I would make sure all video drivers of all kinds are installed, and reinstall the latest forceware drivers. If that doesn't work try a OS reinstall, sounds like a pain but at least it will eliminate almost all software related problems. After the OS install, install the latest forceware drivers and try again. If it crashes still...then it is most likly a hardware problem. Run rivatuner in the background with the temperature chart going for fun again just in case.