If you are experiencing game crashes or your game is slow, here are some helpful tips to follow:
1) Make sure you are running the latest version of Mac OS X as they the latest video drivers for your Mac. Apple for years has provided free upgrades from 10.6 on, so if you Mac can handle it, upgraded to the latest version of OS X is very easy.
2) If your Mac is slow, restart it once in a while. Always try to run games with no other apps open. If an Mac is constantly crashing or mis-bevahing, a restart can sometimes do wonders!
3) If a game is running particularly slow, find the graphical settings in the game and turn down the resolution the game is running at and turn down or off setting like anti-aliasing, etc. This can help improve frame rates within the game.
4) Add more ram to your Mac. The more ram you have, the better today's highly CPU-intensive games will run.