There's a README
that comes with the nvidia drivers which explains the installation procedure in detail. If you followed this and still had problems, try searching these forums for "nvidia", as there are probably 20 questions a day on this subject, and someone else may have already answered them for you
If you did install the nvidia drivers appropriately, then there's nothing else you need to do. 3D acceleration should already be enabled. If in doubt, go to a terminal window (from X) and type:
If they run nice and smooth, then there's nothing to worry about.