I'm running XP Professional and recently installed Sim City 4 with no
problems. Game runs fine. I've done nothing special to the setup of XP
Pro, but I did get to where I am now by upgrading from XP Home after
discovering that the Home verison wouldn't let me talk to a computer that
was a member of a domain. It doesn't sound like much help, but I don't
think your problem is intrinsic to XP.