gaf3:~# apt-get remove --purge gdm
Reading package lists... Done
Building dependency tree       
Reading state information... Done
The following packages were automatically installed and are no longer required:
  ekiga gcalctool gnome-nettool libdjvulibre15 gucharmap industrial-cursor-theme zenity gnome-games esound gnome-cards-data gedit gnome-themes
  guile-1.6-libs gedit-common libdmx1 libkpathsea4 gdb eog gnome-backgrounds bug-buddy vino gnome-keyring-manager evince libqthreads-12 gnome-games-data
  libgnomevfs2-bin zip gnome-core gconf-editor libguile-ltdl-1 file-roller
Use 'apt-get autoremove' to remove them.
The following packages will be REMOVED:
  gdm*
0 upgraded, 0 newly installed, 1 to remove and 29 not upgraded.
Need to get 0B of archives.
After unpacking 16.1MB disk space will be freed.
Do you want to continue [Y/n]? y
(Reading database ... 114407 files and directories currently installed.)
Removing gdm ...
Stopping GNOME Display Manager: gdminvoke-rc.d: initscript gdm, action "stop" failed.
dpkg: error processing gdm (--purge):
 subprocess pre-removal script returned error exit status 1
Scheduling reload of GNOME Display Manager configuration: gdminvoke-rc.d: initscript gdm, action "reload" failed.
Errors were encountered while processing:
 gdm
E: Sub-process /usr/bin/dpkg returned an error code (1)