How to connect to a VNC session through a tunnel using putty
Create a session profile
Use the IP address of the remote computer you are connecting to. The ssh port is 22 by default.
Enable compression to make the session faster
Setup the tunnel options
The default VNC port on Mac is 5900. On linux is often 5900 or 5901. The source port is a free and open port on your local machine. (You may need to open that port on your firewall). The 'local' radio button should be selected. Click add, go back to sessions and save the session for next time. Then login to the remote SSH server as you normal would with your userid and password:
Launch vncviewer
Using a vnc client such as TightVNC, select locahost:50005 (or whatever local port you use):
You will need the VNC server password, naturally. You'll need to ask someone who knows what it is!