I've done the upgrade from 9x to 2000 on a few computers, and it's pretty slick. It will run a compatibility check on the programs and hardware you're running and tell you what will and won't work. You can also uninstall it and revert back to ME if you want.
The only thing is make sure you have a few gigs free on your os drive. 2000/XP is far and away better than ME (which is pure ass).
