Server
If you want to have one desktop to share between all users try vino.
To install:
sudo apt-get install vino
To configure the vino software use:
vino-preferences
Inside vino-preferences
you enable
- Sharing -> Allow users to view your desktop
- Allow other users to control your desktop
You should also enable some sort of security, for example the:
- Require the user to enter this password *****
You might also want to see: How do I enable Remote Desktop connection on Xubuntu 11.10?
Ubuntu Client
On the client machine you also need software to connect to your vino vnc server. Remmina desktop is a good choice as it also gives you the possibility to create ssh tunnels automatically.
To install:
sudo apt-get install remmina
To start: Press WIN + a and select 'Remmina Remote Desktop Client'
Inside Remmina click the pluss icon to create a new connection.
Once opened, eneter your server name and credentials (if you chose password , leav the username empty). Select Color depth : High color (16 bit) and Quality : Good.
Click Connect.
(These options are the ones that have worked OK for me - you might want to experiment with them)
If you need to create a SSH tunnel as well - open the SSH tab.
Windows Client
To connect to your vino server from windows - you have a lot of options.
Try for example real VNC:
http://www.realvnc.com/download/viewer/
Good luck :)