I read this and the armaholic thread, lot's of useful information, thanks a bunch!
After all the tweaks I tried, I am still not sure if I managed to extract the most for my system - 4850 512MB, AMD X2 6000, 4GB or 3 since I am on XP Pro. Latest Catalyst and patch applied. High or Normal Setting at 1600x900 produces pretty much the same rates in the campaign, 20-21FPS. Lowering the resolution or quality form High seems to have no effect, I am still stuck at the same FPS. Tried one of the standalone missions and was getting about 25-26 on High. Something is not right, but I can't figure out what. Is my processor the limiting factor?