LifeHacker has a guide on installing Mac OS X on a PC system:
Two months ago I walked through how to build a Hackintosh Mac on the cheap using PC parts. Since that post, the OSx86 scene has changed rapidly, and now you can install Leopard on your computer about as easily as installing Leopard on a Mac—no command line hacking required. In addition, the resulting installation is—theoretically, at least—can be upgraded without fear of breaking. As if the simplicity of the installation weren't already enough, the new installation tools fix any problems I've had in the past (for example, I no longer need to keep my install DVD in the drive to boot into OS X), and support the Wi-Fi card on my motherboard out-of-the-box. In short, it's a winner.