It can be done through hacking it. It can't be done just buy purchasing the disk and popping it in the computer. However even if you hack it to get it to work on a PC it's not 100% compatible, certain things won't work and most updates break the install so you have to get someone elses hacked upgrade. It works best if you build a computer that closely matches the hardware (brand for brand) components of a mac. It still has to be hacked to get it working but you'll have the greatest compatibility.
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It is. It's a fun thing to do. But as a practical every day machine, it's not worth while.
good article: http://lifehacker.com/software/hack-attack/build-a-hackintosh-mac-for-under-800-321913.php