First, download the latest Nvidia driver (by the time of writing it's version 100.14.11) corresponding to your architecture (i386 or amd64) from the Nvidia ftp site (just look here). Then, make sure the following packages are installed:
- linux-headers-2.6 (corresponding to your kernel)
If everything is set, stop X by typing as root:
Login as root and start the downloaded Nvidia installer (one line):
The installer will ask whether to compile the kernel module. Choose "yes" here. Again say "yes" to invoke the "nvidia-xconfig" script. Now reboot and X should then start showing the Nvidia logo!