Step 1.
Go to
http://www.nvidia.com/object/linux_d..._1.0-4496.html
Step 2.
Follow the instructions!
Basically, download the file from the web page.
If X starts automatically, press CTRL+ALT+F1 to switch to a console.
Log in as root
Close X down with the command init 3 (this switches the machine to run level 3. ie. command line mode)
run the file you just downloaded as per instructions on the web site.
Follow the prompts. You shouldn't have any problems with a standard distribution.
type init 5 to restart X
Done (hopefully)