Same issue here.
Intel core2Duo E7200, same issue with/without OC-ing to 3.1 GHZ
4 GB DDR3
1 week old MSI RadeonHD6850 800/1000
Problem manifests ONLY when AA enabled, no matter which combination of game/catalyst settings.
tried all the combination of the catalyst AA options, combined with the game AA options, *2 (FSAA on/off) *2 (vsync on/off)
Again, ONLY when AA enabled.
Tried to start game without MSI afterburner (hoping it would only be an OSD glitch) but no results so far
Will try an older version of the driver, then will come back.
If this helps, would be a nice news...