I tried it on my XP (well, Kelly's XP) and it didn't work right, I ended up having to roll down a version :/
I think M$ charges way too much for the "upgrade" versions though... It's rediculous... I own like 5 copies of XP home, yet upgrading to vista is still goinna cost an arm and a leg lol...
I think I'm going to start pushing Linux/Wine on people as a windows alternative again lol