Graphical remote login

[stan]

I have 2 Ubuntu machines on the same subnet. On machine "A" which is
running kdm, I configured the following in /etc/kde3/kdm/kdmrc

[Xdmcp]
# Whether KDM should listen to incoming XDMCP requests.
# Default is true
Enable=true

I left the rest of this clause as delivered.

Then I restarted kdm on machine "A". On machine "B", which is running gdm,
I went to the menu in the lower left on the gdm screen, and requested it to
do an xdmcp scan for possible remote login machines. It did not show any.

What I am trying to do is set up so that I can run the desktop (window manager)
from machine "A" on machine "B".

What am I doing wrong here?

-- 
One of the main causes of the fall of the roman empire was that, lacking
zero, they had no way to indicate successful termination of their C
programs.