did you guys read this thread? it appears my overheating theory may have been correct- at least for ati cards. especially in the new iMacs. i guess it always made perfect sense- metal encasement + graphics intense game= overtaxing of chip = overheating of vid card = freeze.
anyone else who is has a pro tower try taking off one side of the case and see if that helps. that's IF you can run the game at all after installing leopard. even if you don't have an ati card i still hold by the fact that the card is being overworked by the game.
https://forums.macrumors.com/threads/383805/