VMware is a great tool for running Windows and Linux anywhere, but OS X clients are not supported. Snow Leopard can be made to run on Windows, and Mac-hacking blog iHackintosh has the nitty-gritty on getting it working.
In order to get Snow Leopard working in VMware, you'll need to be on an Intel-based Windows machine (AMD currently isn't supported) with a retail copy of Snow Leopard, as well as a Snow Leopard VMware disk file, downloadable from many sources (iHackintosh lists a few). The process requires tweaking a lot of settings in VMware, as well as some disk switching and fast finger work, but overall the process isn't too difficult. We talk a lot about using VMware to run Windows on a Mac, which is often the more necessary case, but this is certainly a nice option if, say, you're thinking about making the Mac switch but want to extensively test drive the OS first. Hit the link for instructions on how to get set up.
Install Snow Leopard in VMWARE 7 Windows Edition[iHackintosh]