To run a VNC server on your VPS, you need to have the desktop version of Ubuntu installed. The server version, which you are probably running, is missing some required features.

On your VPS, run the following command to install the desktop version:

Code:
sudo apt-get install ubuntu-desktop
While you are waiting for this to install, download the latest version of tightVNC for your OS (it's free), or another VNC client.

After the desktop install is complete you want to make sure GNOME is installed and configured:

Code:
sudo apt-get install gdm
Code:
sudo /etc/init.d/gdm start
Code:
sudo dpkg-reconfigure xserver-xorg
In order to remotely control the server, you need to install a VNC server. We are going to be using TightVNC, instaling VNC on your server and your computer.

This step will install tightVNC on the server :

Code:
sudo apt-get install tightvncserver
You can now start the VNC. Note: make sure you set a password and remember it when prompted. The password will have 7 character limit:

Code:
vncserver :1 -geometry 1024768 -depth 16 -pixelformat rgb565
If you forgot your password:

Code:
vncpasswd
Go a head and turn off the the VNC:

Code:
vncserver -kill :1
We want to configure it so the desktop environment uses GNOME. Open the startup file:

Code:
sudo nano ~/.vnc/xstartup
And add this line at the bottom:

Code:
gnome-session &
Restart your server:

Code:
sudo reboot
Start the VNC again:

Code:
vncserver :1 -geometry 1024768 -depth 16 -pixelformat rgb565
All of our VNC requests will come from port 590x. The last number is reserved for the desktop number that you assign. We are using 1 (:1) so we only need to open up 5901. If we wanted to start another sever (:2) then we would need to open up port 5902.

On your PC open up TightVNC Viewer. Set the Host to the IP of your server. Set the Display to 1 (:1).
Enter the password that you set when you started the server and connect. You should be remotely viewing your VPS's Ubuntu desktop!