GeForce line of cards actually have the second-best FSAA solution on the market - it's not as fast (in terms of % performance hit) and application-transparent as 3dfx's, but heads and shoulders above Radeon's FSAA in customizability.
For Radeon there's only one FSAA mode available, and that's 4-sample 2x2 supersampling. For GeForce cards following settings are there...
Direct3D
1.5x1.5 "2.25 sample" FSAA: useless, horrible quality. But quite fast.
2x2 4-sample FSAA with standard mipmaps: good quality with reducing jaggies and texture aliasing, albeit there's some critical angles in which some jaggies/pixel popping will be visible.
2x2 4-sample FSAA with double resolution mipmaps: same FSAA quality as above, but with LOD bias equal that of twice higher resolution.
2x2 4-sample FSAA with hires mipmaps and gaussian blur: easily the most usable D3D FSAA setting on GeForces, as fast as standard 4-sample but with superior results. Gaussian blur does a superb work on the jaggies. Some might find the picure a tad too soft, however.
the rest of the settings: there are 9-sample (3x3) and 16-sample (4x4) FSAA modes available. They look damn sweet, but performance hit is horrendous and not very high resolution can be selected without card reverting to a lower FSAA quality setting due to excessive frame buffer memory requirements. Still, it's a mind-bogging experience to try out UT at 320x240/16-sample FSAA - it's like watching a rendered movie, pixel color accuracy is just incredible.
OpenGL
In OpenGL, three first modes from D3D are available. I recommend using mode 3 (4-sample FSAA w/ hires mipmaps).