To learn the basics and different methods of remote desktop, see my previous article.
The most popular way of remote desktop on Ubuntu is using VNC (RFB) but this is very slow because it works by sending compressed bitmap images of your server to the client.
To set up remote desktop this way, goto system -> prefereces -> remote desktop -> select ‘allow other users to view your desktop’ and ‘allow other users to control your desktop’. If you are behind a firewall or router, you have to open up the corresponding ports.
On the client computer, you can download a viewer like TightVNC or UltraVNC. This tutorial can help you encrypt this information through ssh.
However, I found a great alternative called NX. NX works by starting a new X session when you log in. If you have Ubuntu Intrepid Ibex, you can follow this tutorial.