There was an ATI patch to enable AA on SC2. Try that...google catalyst 10.7a. Also, cards are over heating in certain screens of the game, this could be causing the artifacts etc. Just have to insert some lines in an ini file...Google that also lol i can't link it as i'm at work.
my cards arnt overheating thier liquid cooled its was the new ATI paTCH for the 5870 that was messing with my games the 10.7