Verified answer

There is no way to install a "Legit" copy of ANY Mac OS to a PC.

Apple does not license it's OS software for use on anything other than a Mac computer.

First, you are correct that you need a full Retail copy of Leopard (or Snow Leopard) - it won't work with a Restore disk and most of the "patched" or otherwise modified copies online will only work on specific hardware with specific bootloaders (in addition to being pirated).

A buddy and I made a Hackintosh from scratch using the i7 quad and an un-modified copy of OS X. It worked.....mostly. There were some issues with perfials, a few sound card tweaks we had to do, and even now we get a kernel panic about 70% of the time after a reboot so we have to keep it on and in sleep mode all the time. It's awesome and the whole deal was about $1500 (and it's basically a $5000 MacPro with an i7 processor, which Apple doesn't offer) but it's an on-going project and you have to have a lot of knowledge in both system building and OS X to get it to work well, and to deal with issues that come up. Overall it was a fun project but not something I'd do as my primary computer. He's actually thinking of loading Win7 and selling it to buy a new 27" iMac.

We used the RebelEFI bootloader but there are other bootloaders that are pretty easy to use.Just do a little research on the custom build Hackintoshs and decide what bootloader version best fits your needs.

Now, I DID install Leopard on my Dell Mini 9 with no problems what so ever. That little HackBook is killer and runs 100% all the time. I haven't had to do any special tweaks since the first install. I used the NetBookInstaller EFI bootloader and it was smooth sailing. I think I'm going to try with Snow Leopard soon, but it's a slick little beast.

Just do your homework, be ready for things that don't work like they are supposed to, and set aside a lot more time that you think you'll need for the build and install.

You DON'T.

mac osx requires hardware requirements that don't exist on any normal PC, mainly the EFI. Not only that the Mac OSX program will check to ensure it is running on apple hardware.

Yes you can although I'd rather go with linux ;)