Originally Posted by MUYA
ok the low down
NV40 can do AA in modes of 2X, 4X, and 8X (which really is a mixed mode of MSAA and SSAA)
In addition to these, there are other, hidden modes than can only be exposed via a tweaker such as RivaTuner or aTuner. Unfortunately most of those hidden modes can only be used for Direct3D, but they do include 4xS (arguably the best quality mode offered by NVIDIA, better than all ATI modes but at a huge performance cost) as well as three different supersampling options. It gives you a lot to play with, and that's certainly a good thing.