No shit, dude. Where have you been.
FSAA is a feature that has not been optimized for ANY of the nVidia 3D cards (even though it has been available to the GeForce 2 based line of cards). With this feature enabled, you're framerates are most definitely going to be slow. (However, did you notice how good the image quality was? Very little zaggies.)
On the other hand, FSAA IS much more optimized for the GeForce 3 line of video cards. Without a GeForce 3, I recommend never turning FSAA on, unless of course you want to watch a slide show.
Hope this helps.