Its has been possible for couple of years now:
http://wiki.osx86project.org/wiki/index.php/Main_Page
Also known as hackintosh. Besides the above wiki you can also check out their forum for support for DIY.
http://www.hackint0sh.org/forum/
Here is a lifehacker guide in 2007 (might not apply anymore):
http://lifehacker.com/software/hack-...800-321913.php
Gizmodo guide made this year hackintosh guide on dell mini netbook.
http://gizmodo.com/5156903/how-to-ha...e-os-x-netbook
Also
http://psystar.com/ sells non-apple desktop computers with OSX installed.
As for my personal experience, I have tried to install it on one of my computer 2 years ago, with not much luck (I went up to login screen and it started rebooting in a loop). But a lot changed in the last 2 years and its (supposedly) a lot easier. But still not for the faint of heart - if you don't mind tinkering with stuff and have enormous amount of time doing it, you might wanna give it a shot.