I tried running the Radeon under Mandrake 7.2 for a week and could not get it to work. XFree86 4.0.2 has built in support for the Radeon, but it just wouldn't work for me. I put my GeForce 2 MX back in and was playing Quake 3 and UT with exceptional frame rates within two hours (complete reinstall of OS included). As for Win2K, many people claim to get a boost when they go from Win9x to Win2K with their NVidia cards. I know I was getting excellent scores with my GeForce 2 MX in Win2K. It blew away my Radeon at 800*600 and both cards were even at 1024*768. Just to give an idea of how the frame rates were on my TBird 700, I scored about 77 FPS with the Radeon at 800*600 and all the good on, including highest visual quality set in the drivers (Timedemo 1 on Win9X). I scored 102 FPS same settings on the GeForce 2 MX in Win2K! At 1024*768, same settings, both cards score approx 65 FPS on my system. The Radeon and MX were clocked to 183/183 and 200c/210m resp.
To make a long story short: GeForce cards are better in Win2K and most definately better for Linux in my experience.
EDIT: Grammer