Well, I've yet to isolate my issue with my computer randomly freezing during graphic intensive gameplay, so I suppose I'll settle with trying an OS reinstall. Only problem is, I previously installed the OEM version of XP from newegg, and I'm wondering if it will reinstall from the same disc, or are OEM discs 1 shot deals? I won't proceed further until I hear back from ya'll, but while I'm at it, maybe you can help me resolve the issue. I recently purchased an EVGA 8800GT and am having a little trouble playing games like CoD4 and etc. I came from an X1950PRO so this is a little bit of a disappointment that the 8800gt is failing in comparison at this moment. Everything seems as if it should be working, and yet after about 30 minutes of playing, my computer randomly freezes. I've never received an error message as the freeze generally forces me to reboot manually. I'm running on e2160 OC to 2.7, 2gb OCZ ram, Corsair 450vx 450w psu, and Gigabyte P35-DS3L. Previously I had no issues running any of my games with the x1950PRO and the 8800GT still wont last even on the comparable settings. I uninstalled all of the previous drivers correctly and used drivercleaner, so I doubt that is the issue. My temps are fairly cool, the CPU idles at 30c, load about 45c and the GPU idles near 50c, load 60c. All of the existing hardware is practically new, 3 months old, and appears to be in working order. Furthermore, the graphics card seems to be the culprit, yet it runs with flying colors during the brief time it actually works during games, with an additional 12,500 3dmark06 score. I've tried multiple fixes, yet nothing seems to work, so I suppose it wouldnt hurt to try a complete reinstall. If the reinstall seems like my best option please respond, I'm looking for any and all advice.

the oem can be installed many times.
the problem is your power supply, not enough power. thats what it sounds like to me anyway.

yep.. same to me... try the Corsair Hx520... or something like that...

Try putting a fan on the side of the computer and playing.
Check you GPU temperature while playing with no extra fan.
There is a bios update for the EVGA 8800GT that resolves fan issues.

The issue could also be bad memory or a failing power supply.

These things (as you know) can be tricky to nail down. Your power supply assuming its working correctly will have no bother powering your system.
As its a newish system and all you have changed is the graphics card it strongly suggests to me that it is the card at fault.
It doesnt hurt to RMA it (Hope you still have the 1950 to put in while its gone). If you do still have it or can scrounge a borrow of a spare one then reinstall another card, If you don't get the problem then its the card.
Truth be told it could be a number of things on the card or in your box. Your temps are fine, its possible that its Ram or PSU related but again with the age of the hardware there's more chance of it being the card.
Mactronix

The very first thing I would do is remove the OC and run stock… Then try to crash it again.

If the issue persists move on to the other things everyone mentioned here.