Man dude you got google, you got game reviews, you got everything to research even then you come here with your crap questions. No offense intended. Anyhow the game does not support AA, even if you change the setting from outside like Nvidia's settings in which you can set all games to have 4x AA. This game wont have any, its just a great game of 360 ported over to PC with a crappy work.
My 6800GT could run the game ok at 1024 reso with medium textures. The game required a 512MB card to run at high settings/textures. Its that way only and you got a card which got that much ram in it. Now to sums things up, the game is diffcult, slow and frustrating and you specially wont enjoy it with all the jaggies around the place.
X1900XT"X" as you said before can run every game right now at 1280x1024 without coughin up a fur ball, so enjoy it. GRAW is an exception, it is meant to choke. I thing the proccy will bottleneck your performance but thats just what i think... The game is shittingly frustrating, took me 1 week to complete it.