Using -L on the command line with SSh will bind a remote port to a local one. For instance, if you wanted to tunnel the port for a remote desktop (usually 5901) to a local machine, you would type the following

ssh -L 5901:localhost:5901 remote_ip

You could then access your remote desktop by connecting your VNC client to port 5901 on the local machine, and the data for the remote desktop would be tunneled through the SSH connection.