Hadrian has done some experimentation lately, and he's also got some good screenshots of the differences between Wing Commander Prophecy with and without Full Screen Anti-Aliasing turned on. FSAA is one of the newer technologies available on the latest generation of 3D acceleration cards. These shots were taken with a GeForce 2 MX. I just picked up one of those cards myself, so I can't wait to try it out. Note that while FSAA can provide a substantial improvement to old games that weren't designed to take advantage of today's modern effects, there is a limit. Prophecy and Secret Ops are probably the only two games where you'll be able to get this benefit.
You can click on those for full screen images, but the area in question is the same in the thumbnails. You should be able to tell that the image on the right is a bit smoother. It's not a super major improvement, but I'm surprised that they have technology that can do that. Pretty neat, huh? You should be able to get this benefit from a Voodoo 4/5, a Radeon or any GeForce 2.