One other thing to check is to make sure you've got the latest drivers for your video card. Microsoft DID NOT test all video drivers with XP prior to releasing XP. I had the same problem and it turned out that the video drivers for the ATi Radeon card included with XP were the problem. I went to ATi's website and found they had new drivers for XP posted. I donwloaded and installed them and the problem went away. XP WILL initiate a reboot if the system is using a "bad" video driver. Microsoft has recognized the bug in the kernel source code and is planning to include a fix in Service Release/Pack 1, due out this spring.