I'm currently running P7 on XP 64 Pro and (so far) it seems to run okay (other than the occasional crash-to-desktop-with-no-errors). Loads up and renders faster than Poser 6 did (also had that installed on the same machine as well). I will add that my system is a dual-core Athlon64 with about 4GB of ram installed so I can't guess what performance would be like on a slower machine. But otherwise, you really shouldn't have that much in the way of problems :)