I don't know if you've heard about this.
It turns out there is a huge problem with NVidia graphics cards if you install SP2 on your 64-bit XP.
Essentially you get a BSOD with the following message: The driver is mismanaging system PTEs.
I had a problem with my Nvidia 7800 GTX and XP64, though when I bought XP64, the program was with SP2. I found that by using an older driver, there was no problem. It seemed that when Nvidia made the newer drivers, they made things worse, not better. I later bought a 8800 GTS 640 and it didn't work any better. I eventually switched to an ATI card and there has been no problem. Nvidia really needs to do something right with their drivers, in my opinion.
Guess I'm just too bloody lazy. I've been running XP64 and an NVidia 8800GTS-640 for over a year now. When I first power the system up, it boots up fine. When I attempt to start an application, it BSODs and reboots. At the moment, I couldn't tell you why it BSODs or what error causes it. I never bothered with it because after the reboot, the system runs smooth as silk.
Guess I'll take a closer look when I get home and see if it's the same error folks have been experiencing.