To access the unsecured(!) Remote Desktop of an Ubuntu 9.10 installation, you need following:
First, install the openssh-server:
sudo apt-get install openssh-server
Then, you need to enable the XDMCP Server.
That became a bit tricky on that Installation, as the "Point 'n Click" enabling has been removed.
Dunno why. So, thats how it works. First we copy over the "empty" custom.conf for gdm:
sudo cp /usr/share/doc/gdm/examples/custom.conf /etc/gdm/
Then we edit it:
sudo vi /etc/gdm/custom.conf
It should look like this in the end:
# GDM configuration storage
[xdmcp]
Enable=true
DisplaysPerHost=2
[chooser]
[security]
[debug]
After that, we need to restart gdm:
sudo restart gdm
And thats it, the XDMCP is running. To access it on Windows i.E., you have to download Xming ( http://sourceforge.net/projects/xming/ )
Download and install the Windows Client, start the XLaunch Tool. Choose One window, Next, Open Session via XDMCP, Next, Enter the IP of the Ubuntu Server under "Connect to Host" and Press Next, Press Next, Save the Config were you want to have it and Finish.
Thats it, an X Window with the Login to your Server will open. Please bare in mind that this XDMCP Session is NOT encrypted. You should Tunnel it via SSH...
// Big Parts were taken from http://www.peppertop.com/blog/?p=690