Did you literally do an upgrade, or a wipe and clean install of XP, I have always had bad experiences with upgrades, I have yet to see m$ do one right.

I have had a similar experience upgrading from 98 to 2000 at work. Except in my case, I could open task manager and watch the CPU usage meter "toggle" from 1% to 50% every 2 secs.

IMHO I recommend a clean install. Upgrades just are too finikey.