I have run both and havent really noticed any performance increases in Poser with one over the other. WindowsXP, which I am using now, has an overall better interface, but still has its share of bugs. I just dont like the way it dumbs everything down like we are all a bunch of idiots. And there is a lot of extra crap that you not only dont want or need, but actually wish was not there. Windows 2000 is a good operating system, but if you dont know quite a lot about computers then XP is probably a better choice for you. I havent had too many problems with it yet.