I had an issue where my cordless mouse drivers were not compatible with an update, and it went BSOD on me. If I had known, simply installing the newest version of the software (along with its updated drivers) would have prevented that.

In my case, I had to login into the Win2K install using an emergency disk, and simply delete the offending driver. Then the computer booted, and I downloaded and installed the newest software for the mouse. No trouble after that.

Basically, since you didn't install any new hardware right after you upgraded, I would check to see if any software you had installed should have been updated first (mouse, printer, scanner, video, sound, etc.). If I came up with another suggestion, I'd also be taking a stab in the dark.