Unfortunately, getting AA to work effectively in stalker is not easy, at least in my experience anyway. As far as I know, AA is hard coded to the engine, making it more difficult to get working the way you want. The only game out of the three that I found to be the exception was Clear Sky (when you selected x4 AA in the menu you got just that). My advice would be to contact Dezowave directly on their forum. Let us know how you get on.