Dogtags, I'm not sure your success is idicative of others... I have the radeon 4870, like one of the above posters on this page:
"I've also got the same issue, postprocessing is turned off, and there is absolutely NO difference between disabled AA and High AA on my system, I'll try his work-around, even though it's not a preferable solution, it may work."
--I also have the same issue, I got AA to work ONCE, and that was after an hour of doing a voodoo dance of turning off/on postprocessing, rebooting, praying to the rain god, and then OMFG I had AA, no more jaggies... Took a hit on framerate prettybad so I tried to tone it down a notch to normal---wait, what?! Nothing happened!!! It stayed on high!...Tried to turn it to low, same thing, AA STILL THERE! then I tried to turn it off, and once again, AA, so I restarted the game, and BAM! No AA, and haven't been able to get it back since...
::grumbles:: I've not spent more than an hour playing vs about 10 hours trying to work the settings out...
I have a Radeon 4870, 3ghz dual core processor, 4gigs ram. "