8x AGP should be enabled automatically if your mainboard supports it. You can check the status with this command:
It would be helpful to know what kind of motharboard you are using if you are certain that 8x AGP should be enabled.
FSAA and anisotrophic filtering are enabled as environment variables. This can be pretty inconvenient, but better than nothing... If you're using bash, open an xterm and try this:
For csh or tcsh, try this:
setenv __GL_FSAA_MODE 5
I suggest using YanC
, yet another nVidia configurator.