Apple Thoughts: Run Windows App With Wine

"There are many options for running Windows programs on the Mac. Boot Camp, for instance, is included with OS X for installing Windows on a separate partition. Parallels, VMware, and Sun offer virtualization software that let you run your Windows programs without logging out of OS X. And then there's Wine."

This Open Source application layer runs "within" rather than "stand-alone" outside of OS X. What that means is that you don't have to actually own a copy of Windows to run Windows programs since Wine implements the Windows API. There is a tutorial located here that David Baumgold put together, covering every aspect of using Wine on your system. Be forewarned though, you need to have some knowledge of using Terminal.app as the install is pretty technical and should not be attempted unless you are sure of your skills. There is also a list here of compatible programs that work with Wine, and if you aren't sure you want to mess with Terminal, head on over to Crossover and get their application that makes it easy to install Wine.