Curious. Could you post the contents of your /etc/X11/xorg.conf file?
That said, everything you *should* need to do would be:
$ sudo su
# mv /etc/X11/xorg.conf /etc/X11/xorg.backup0804
# aptitude purge ~nnvidia
# dpkg-reconfigure xserver-xorg # to regenerate one
# aptitude install nvidia-glx-new
# nvidia-xconfig -d 24 --allow-glx-with-composite --add-argb-glx-visuals --randr-rotation
If it doesn't work,, do a safe boot and then post the contents of your /var/log/Xorg.0.log.old file. Better yet, choose to go back to the terminal in the bulletproof X menu (or by picking recovery mode at boot), enter this command, scroll down until you find a line that says 'Driver "nvidia"' and change it to 'Driver "nv"'.
Ctrl+O to save, Ctrl+X to exit. Don't forget the log file if it doesn't work.
$ sudo nano /etc/X11/xorg.conf