I think that there have been many people that have had problems with this before so I thought that I'd write a tutorial for it.
I'll start off by saying that you need to know what version of XFree you have and if you have more than one. To do this go to /etc/X11 and look at how many XF86Config files you have. I have a XF86Config and XF86Config-4 file in there because I have version 3.x and a version 4.x. If you have the same thing, edit the XF86Config-4 file. If you only have an XF86Config file, edit that one.
Now enough of that, let me give you the steps:
*NOTE* If you have a bad memory you might want to print this out before making the drop to run level 3.
1) Download the NVIDIA Drivers.
2) Drop to run level 3 by opening a terminal, signing in as root by typing su and then the password.
3) Change to the directory of the Download. if your home is on /home/username and you have a Downloads folder containing it, type cd /home/username/Downloads
4) Type sh file_name_of_driver_file.run
5) Follow the instructions for installation.
Now it is time to open those configuration files I was telling you about. You'll have to be root to edit them, so open a console and get root privalages by typing su and the root password(if you forgot how to do it
) Change to /etc/X11 and open the file with your favorite text editor. With gedit, type gedit XF86Config-4 (or whatever config file based on what I addressed earlier). Now, find the line that says Section "Device" and make it look like this:
VendorName "nVidia Corporation"
BoardName "NVIDIA GeForce3 (generic)"
Please note that if you don't have a GeForce3 you should change the BoardName to the one you have. It should work fine anyway though, but I'm anal retentive like that.
Now, find the Section "Modules" line, and make it look like this:
Load "dbe" # Double-Buffering Extension
Load "glx" # 3D layer
Now, restart the X server to see if it worked. If it worked, you'll see the NVIDIA splash screen at the start of the X server and should be able to run OpenGL games much smoother.
I hope this helps you with this part of getting things going.