Do you have your system automatically reboot on a system failure? Go to the System applet in the Control Panel, look at the Advanced tab and "startup and recovery." You'll see a place where you can check "automatically reboot." If you uncheck this box you'll be able to see what program is causing the problem.
If the problem is with a service that is set to automatically start, one way to fix this is to boot from the Win2k CDROM and load up the Recovery Console. You'll see what looks like a command prompt and then you can disable the service that is causing your computer to crash. I don't remember what the exact commands are but if you type "help" or something like that you'll get a list of commands you can use.