Check out PearPC
Here are some comments on PearPC from djeddiej :
First of all, before you do this, you should install Mac OS X using a legitimate copy of the software. It is after all, a nice OS, and if you want to use it for many purposes, such as web-page testing, but don't want to shell out the money to buy an entire Mac, then this may be a viable option for you. As of this point in time, the EULA states that you can install Mac OS X "onto an Apple-labelled or Apple-licenced computer.", so the lawyers were not too specific - place an Apple sticker somewhere on your PC. (I had a lawyer review it to make sure).
Secondly, your PC should be powerful enough to run it. For hardware, you should be running a Pentium 4 2.0 gHz or higher machine with at least 1 Gig of RAM (a minimum of 256 Megs of RAM will be set aside for Mac OS X when it installs successfully).
It is recommended that you install it on top of an OS that has the minimum installation requirements, no extra screen savers, games etc running on it. PearPC with MacOS X can install on top of both Microsoft Windows and Linux-related Operating systems (you may need to a little search to see how other people have done it). Follow the guides available at the aforementioned sites carefully, and you can run Mac OS X on a PC!