Have you been under a rock since 2006? Now you can run Windows and OSX out of the same box, of course you can play games.
Sorry, I mis-spoke. That should be "OS X", not "mac". And I'd like anyone to show me a good current game that can be played in a mac. Even the newest EA releases require a dedicated graphics card, where as their Windows counterparts don't.. so I don't get it. Unless you already need a Mac Pro (and chance replacing the whole thing every time a new high end graphics card comes out), I don't see the advantage of a Mac Pro over a low end mac and a gaming rig.