when you go into the gui (what desktop do you run, anyway? gnome? kde?), do you see the nvidia logo splash screen?
if not, then....
as root, do this command in a console (in kde, you can start, run, konsole)
lsmod |grep nvidia
note the pipe character (shift backslash on my keyboard)
if you don't see something similar to:
nvidia 1669728 10 (autoclean)
then you haven't gotten the drivers loaded.
you'll have to:
if you DO see output like the above, then the drivers are loaded.. next, do this command:
(expect to see some animated gears)
glxinfo |grep direct
expect to see...
direct rendering: Yes
this will at least tell us if opengl is running.
also, read the quake3 readme!
cat /usr/local/games/quake3/README-linux.txt |more
it should explain that you need to copy a file or files from the cd to complete the install.
report back your findings and we'll try to help you a bit more