Did you install the Nvidia drivers?
Well, just open a terminal (Konsole, xterm, gnome-terminal, whatever), and enter 'glxinfo'.
If the output contains [...]Nvidia Corporation[...], you should have 3D hardware accelleration working.
"Computer games don't affect kids; I mean if Pac-Man affected us as kids, we'd all be running around in darkened rooms, munching magic pills and listening to repetitive electronic music."
-- Kristian Wilson, Nintendo, Inc, 1989.