If you already have an XF86Config file working with a different driver
(such as the 'nv' or 'vesa' driver), then all you need to do is find
the relevant Device section and replace the line:
Driver "nv"
(or Driver "vesa")
with
Driver "nvidia"
In the Module section, make sure you have:
Load "glx"
You should also remove the following lines:
Load "dri"
Load "GLcore"
if they exist. There are also numerous options that can be added to
the XF86Config file to fine-tune the NVIDIA XFree86 driver.