Members of the OSx86 Scene forum have been discussing a technique to modify Leopard to run on PCs. The method requires a PC that has SSE3. The technique violates the Mac OS X license.
The version of Leopard used was the GM, 9A581. The cookbook-like instructions involve command line work, patching an image of the install disc, burning a new disc and then installing on the PC. Thatis the short version. The actual instructions are several pages long and require one to be very familiar with UNIX.
While there may be some debate about the legalities of unlocking an iPhone, state and federal laws, and so on, this is one gem that Apple protects very tightly because Mac OS X drives Appleis Macintosh hardware business -- a business thatis many, many times larger than their software business and one which Apple can be expected to protect.