Parallels, an Apple hardware XP/Win2K/Linux virtualization engine built by a Russian team (I like it), makes it possible to run OS X on generic Intel hardware:
Parallels and VMware running Mac OS X on XP? - The Unofficial Apple Weblog (TUAW)
... SWsoft's Beloussov says that this spring, Parallels will upgrade its software further, in a way that by coincidence will make it easier to run Mac OS on a non-Apple computer. He also insists that is not deliberate, but just a consequence of the nature of the technology, especially now that Intel builds virtualization technology into its chips. ...
This is bad news for OS X security. One of the reasons I run my Macs without corrosive antiviral software is that Apple hardware is too costly for non-professional crackers to buy, and the pros haven’t seen revenue options in the OS X world (OS X default security makes it harder to write reliable spambots, businesses don’t run OS X). Virtualization will allow the amateurs to enter the market, and even the pros will start to experiment.