it's as simple as that: original 3dfx Tools were made for win 2000 (i bet you installed the win 2000 version), and win xp hasn't been published when the latest 3dfx drivers were published, so they aren't compatible. try looking at the falcon fly drivers archive, there you may find some modified 3dfx drivers which you can install on win xp (well, I was too lazy to get my voodoo5 working well under win xp and so I'm still running win 2000 with service pack 4 -> fine game compatibilty)