According to MacBidouille (1, 2), Apple's Mac OS X x86 developer kit can run on any Intel based PC. However you have to make some mods or use VMware which will emulate the proper environment required by Apple’s developer kit.

There are three requirements to run the kit on any PC:
- the Intel TPM chip presence
- the support of SSE3 technology (present in recent Intel processors)
- the graphic chipset must be a GMA900 so that Quartz works properly

VMWare is capable of running the kit without any problem because it can emulate the required PC but VMWare will provide poor performance.

There are, however, already work-arounds (in the form of patches) to run the kit on any PC but. However at the moment they aren't very stable, especially if you use the work-around for the SSE3 support.

MacBidouille claims that some people can run Mac OS X x86 developer kit quite fine on their PC, with iTunes and iPhoto (with digital camera connected) running flawlessly.

Readers have reported that the kit is already available on many BitTorrent sites either as DVD image or as VMWare-ready volume.

UPDATE: MacBidouille now provides a torrent with two videos showing Tiger running on a PC.