I haven't been able to force anything more than what looks like 2XAA either.
Would be good if they had someone on hand who could implement that new kind of anti-aliasing nVidia have developed, as mentioned here -
http://forum.1cpublishing.eu/showthread.php?t=24658
From what I've read about the way game developers can choose to use it, it looks like it could be a solution to the shimmering that's always been a problem for long-distance landscape views, as well as a more fps friendly way of doing AA in general.
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"...Before that i think Oleg had said COD uses a "special" in game version of FSAA that nobody had used before..." - Furbs.
I don't remember hearing about that, just about them meeting with nVidia representatives once for some unspecified reason, way back when. Would be funny if it's the same thing I referred to above, but they haven't got it working properly or it's limited somehow. The fact that AA can't be forced by the usual methods suggests to me there might be something different going on, if it's not just broken because of their other DirectX Full-Screen problems, or for some other reason.