I'd suggest you pay a little more attention to the detail in some of the
previous posts. ie. If you 'just want X working', get the vesa driver working.
This is probably what Ubuntu was using...it wouldn't have had 3D acceleration.
Anyway, your last error (
http://justfuckinggoogleit.com/) is simply because
you don't have the kernel-headers for your currently running kernel.
$ uname -a
will tell you the exact version you are using.
# apt-get install kernel-headers-2.6.11-9-amd64-k8
is the sort of command you would use (depending on your kernel version)
You may find that the nvidia drivers complain about the riva module
being compiled into the Debian kernel. The simplest fix for this
is to add a line like this in your lilo.conf (prob. similar for grub)
and reboot.
append="video=rivafb
ff"
My final suggestion is to install and run xdebconfigurator
# apt-get install xdebconfigurator
Hope you win soon.