I'm running XP Home Edition and while I noticed slower performance than P4 w/PP before I installed the first patch, it seems to be better now. I haven't noticed slow rendering times and I've only been using the Firefly Renderer. One thing I do when full tracking slows down is to switch to a less memory intensive display style like wireframe or lit wireframe when posing and turn on the texture shaded mode only to "proof" you pic. These display modes use less system resources. Millieum figures can certainly slow things up quite a bit but are worth it as far as I'm concerned.