Can't use AA on Far Cry 2?

So I'm pretty sure my machine could handle 8X AA or at least 4X AA on Far Cry 2, I mean I run every other game on ultra high settings even Crysis. Could it be a driver issue? I'm using ATI 8.12.
Here's my rig:
Intel Core 2 Duo e8400
4 GB DDR2 800 Kingston HyperX
Intel DG35EC Mobo
Corsair 450 watt psu
Asus EAH HD4850 TOP
It's really buggin' me, I mean the game still looks great but I get annoyed easily.

You have to be at 1024 or 1280 resolution then?

I found that with a 4870, turning on U.High shadows kills my FPS. I have to settle for U.High everything except shadows set to V.High with 2xAA for one 4870.

8xAA with two of my 4870s drags it down to unplayable...you won't hit 8x with one 4850. 4x even on one 4870 IMO is not very smooth. You are setting your sights too high there champ.

It also could be a driver thing if you don't fully uninstall your previous versions but.....8xAA with one 4850 is asking for too much

Edit: Oh yeah, also make sure that you aren't going through CCC for AA. It doesn't do crap yet it hits your FPS still. I set all of the AA setting to use application settings...it helps up your FPS.

On my machine I use a 22 inch widescreen monitor, so I have the resolution set to 1680 x 1050. Even so Crysis is fine and I know for a fact my machine is more than capable..I'll deal with it, but I can find a way around it. I know turning the res down makes it run smoother and I can put the AA on then but It doesn't look as good y'know?
To be honest you don't need that powerful of a machine to run games nowadays, my brother has a p4 extreme oc'ed at 4 ghz and the same graphics card as me with only 1.5 gb ram and he's running Crysis as good as I am on the highest settings.

I have XP Pro SP3 so yeah I'm using DX9