have you tried using
if so, is "x-window-system" installed?
if not then use
apt-get install x-window-system
the next thing is to see if you have a window manager installed. you probably would be using kde or gnome.
you would have to see if they are installed.
if it says that the current version is already the latest version then X is installed and you will need to check your XF86Config-4 file. search around the forums to find some help on that. there have been plenty of people that have asked how to config it.
if none of this helps then look in my sig and use the easy debian install instructions to restart and get the system up and running the way you like.
for a list of debian apps go to http://packages.debian.org/stable/allpackages.html