Ive tested this in multiple games(Alien Swarm, Empire Total War, Dawn of War 2) and even on the ATI catalyst control panel itself. Whenever I enabled AA of any level, whatever, my screen will freeze, and go to black, then come back a few seconds later, back to black, etc... until I eventually get the program closed or just reboot.
Ive uninstalled and reinstalled videocard drivers both old and new(tried 5 different versions so far) and used driver cleaner inbetween installs to ensure I did everything properly. I also have the latest version of directx and im currently running the newest ATI drivers which I installed this morning.
Whats interesting though is that other than that aspect, my system runs amazing. I played all those games I lsited on high or highest settings with zero problems, unless I try to enable AA even when the rest of the settings are at the lowest.