This solution will cost you money, but it'll probably be the best one if you want to play games on a mac.
VMWare has a program called VMWare Fusion
(link). It costs $79.99 (USD), but it's worth it. It runs Windows as a virtual machine on your computer, so you can run Mac and Windows clients side-by-side. This is even better than partitioning your hard drive with a Windows install.
I know paying for something like this isn't what you're probably interested in, but it lets you run almost any Windows application, so you'll be able to play all the games the rest of us can.
Off topic, but... why do you want to use a Mac over a Windows machine?