I know for a fact you must be using an Intel CPU to run OSx, although I'm not sure about the GPU/Chipset ect..
GPU, chipset, sound, wireless, ethernet. I'm quite sure it all comes into it.
I think unless you've got the same components that you find in a Mac, you could have difficulty in making things work. If you're going to do a
Hackintosh, i.e. running OS X on a non-Apple computer. You have to chose your hardware very carefully.
Plenty of information here...
http://www.hackintosh.com/
For obtaining Mac OS X, you can just walk into an Apple Store and buy it, it's not even expensive.
As for the legallity of running OS X on a non-Apple computer, it certainly violates Apple's OS X
click-through EULA. IANAL but click-through EULAs have no meaning in law, therefore is not illegal to run Apple's OS on a non-Apple computer. However Apple have made it deliberately difficult to run OS X on a HP or something. So one will have to do all kinds of hackery to make it work.