If you're going for a gaming Mac, then the general rule of thumb would be not to get one with integrated graphics. This means not to get one with a 9400M GT (the exception to which could be the higher end Macbook Pros which also include the 9600M GT which has dedicated video memory). It would also be wisest to install Windows on a partition for games which cannot be played on Mac OS X....
Your best choices are the Mac Pro (expensive, don't pay for extra RAM, it's best to add it in yourself), the Macbook Pro (Get one with the 9600M GT, and don't purchase more than 4 GB of RAM), or one of the higher end iMacs (One without a 9400M GT)....
Also, do yourself a favor and don't capitalize the whole thing...
MAC usually implies
this, while Mac refers to a computer built for Mac OS X...