Sometimes after this has happened Direct3d will stop functioning. DxDiag will report that no D3D device is present and other games will give an error message stating that the Direct3d renderer could not be found or initialized. A GPU monitoring program called GPU-z gave me the impression that the video card had turned off or something as all of the sensors were blank.
The other way it crashes is if after about 3 minutes (but before the screen has frozen) I open any containers or bring up the pipboy the screen will freeze, pressing escape will trigger the CTD and my video driver will crash (at least I think that's what is happening). I'll briefly end up on the desktop in a very low resolution, possibly 640x480, and 8-bit colors. The screen will flash and then my monitor will go into sleep mode and wont wake up, forcing me to restart the computer.
This is the only game that causes this problem for me. Other more graphically demanding games (crysis 1 and 2, assassins creed 2, fear 3) run better than fine even on my old hardware. In addition Fallout 3 runs just fine on my computer.
I should also mention that I have tried lowering all settings as low as they go and raised them as high as they go and this doesn't change the stability of the game at all, the time frame for crashing remains the same.
The innards:
Asus A8n VM CSM
AMD Athlon X2 3800+ 2.0Ghz (2x1.0ghz cores)
Nvidia Geforce 9800 GTX+ 512mb (drivers up to date)
4x512mb Corsair RAM
Corsair TX 650w Power supply
Windows XP 32-bit SP3
Up to date directx 9.0c
Possible "problem child" is my sound card which is older than old but has never given me any issues and provides some excellent sound quality and options. Its the SoundBlaster LIVE! Audio c800. They haven't provided updates for it in a long time but they did release a kind compatibility driver package so it would work properly on newer systems.
Edit: Forgot to mention that when I checked the Windows crash log the crash was listed as a c0000005 access violation in FalloutNV.exe.