The bloggers at Profit42 posted instructions that they claim will get the upcoming version of Mac OS X, code-named "Leopard," running on generic Wintel hardware. Two catches: It's illegal to do, and they won't tell you where to get the software, because that would be illegal, too.
The bloggers write:
DISCLAIMER: This guide is for information purposes only! We only say what's possible. As you maybe already know, it is illegal to download OSX 10.5 Leopard and illegal to install OSX 10.5 Leopard on [your] Windows computer. If you are here for that purpose, leave this site now. If you want to use OSX, buy a Mac (I would recommend the iMac that has been released a few days ago, it's fast and the design is just ... well, let's say it's prettier than the girl you met yesterday).
Wikipedia has a history of Mac clones. Apple sanctioned clones 1995-97, but Steve Jobs ended the program when he took back control of the company.
Wikipedia says there was an earlier clone program:
From 1986 to 1991, several manufacturers created Macintosh clones, including the portable Outbound; however, in order to do so legally, they had to obtain official ROMs by purchasing one of Apple's Macintosh computers, remove the required parts from the donor, and then install those parts in the clone's case. This resulted in very expensive, relatively unpopular clones.