NVidia supply an installer for linux - did you use that?
There is also an "install-nvidia-debian.sh" script for kanotix.
Possibly like this:
As root in a textconsole [ALT-CTRL-F1]
# echo xserver-xorg install|dpkg --set-selections
# init 3
# apt-get update && apt-get dist-upgrade
# wget -Nc -O/usr/local/bin/install-nvidia-debian.sh http://kanotix.com/files/install-nvidia-debian.sh
# chmod 755 /usr/local/bin/install-nvidia-debian.sh
# init 5
... I think ...
To force the vesa driver, I think you just type "vesa" at the boot: prompt
Of course, whenever you edit a default (working) configuration file, you should always create a backup, in this case: "cp xorg.conf xorg.conf.old", before
This way, should anything go wrong, all you gotta do is "cp xorg.conf.old xorg.conf" and you have a working x display again