This is the SSH part where you connect to the remote system and send a local port back to you:

ssh -L 5900:localhost:5900 -p altsshport user@domain.com

What can you do with this?
You can run a service on your remote system like this:

x11vnc -display :0 -localhost

On newer Xubuntu systems, you might have to do this script. It will make it easier to start.
file:

startvnc.sh

script:

#!/bin/bash

x11vnc -display :0 -localhost

# Include this at the end of the line for 2/3 scale
# -scale 2/3

Then, you can vncviewer to your local system:

vncviewer -bgr233 localhost

Voila! Your remote system VNC over SSH in 8-bit display inside an encrypted tunnel!