What Debian are you using ? Because Sarge dosent use the same X systeam that Etch and Sid does, Sarge uses Xfree86 and Etch and Sid uses Xorg.
Well If you are using Etch or Sid you may do
#apt-get install xorg* xserver-xorg*
I hope you solve this problem, after you install all this packages you may want to install:
#apt-get install kdm kde
This will take a while, about hours ! But you-ll see the results