If it's an Intel-based Mac, you can download/run a utility called "Boot Camp" which will allow you to run Windows on your Mac (you will need a valid copy of Windows to install, mind you).
There's also a program called "Parallels" which allows you to run Windows on an Intel-based Mac concurrently with Mac OS X (Windows runs in....well....a window).
If you have an older Power PC Mac, you can do the same with Microsoft's Virtual PC.
Good hunting!