FreeNX (http://freenx.berlios.de/) is a Terminal Server for Unix & Linux, similar to windows remote desktop \
or linux 2xTerminalServer. It is based off the non-free NX (http://www.nomachine.com/index.php). \
FreeNX client is only for linux, but NX has free clients for windows (http://www.nomachine.com/download.php)

Install[-][--][++]

http://www.drtek.ca/freenx-server-ubuntu-hardy

Note, uses SSH, so uses that port in /etc/ssh/sshd_config
also, in sshd_config, if you have the AllowUsers set, then must add nx
ex: AllowUsers nx ubuntu john joe

Install Ubuntu Karmic[-][--][++]

https://help.ubuntu.com/community/FreeNX

sudo add-apt-repository ppa:freenx-team
sudo apt-get update
sudo apt-get install freenx
sudo /usr/lib/nx/nxsetup --install 

Note this installs a ton of extra packages, so I wouldn't do it on a minimal server installation.