I wouldn't bother with Crossover for anything (not the "games" version nor the normal applications version). It's only of any use if you have REALLY REALLY simple requirements and the game / application is (supposedly) well supported ... even then it's buggy and slow.
To really play Windows games on a Mac you can use VMWare Fusion or Parallels Desktop, but even then these aren't particularly designed for gaming, especially those that need 3D graphics cards (which is almost all games these days). For real gaming you have to use Apple's Boot Camp, which gives you an almost 100% real Windows computer, although you do have to reboot it to swap between Windows and Mac OS. For any of these three option you'll need to buy and install a proper license for the version of Windows you want (XP, Vista, etc.).