there is also another way to get this working.
many ssh-clients let you configure the port to use
on the router you have to configure nat (or better pat) to translate the ip adress to the one of your target machine and the destination port of your target machine.
this setup is a bit more work to do but it reduces network trafic in the target LAN
this setup can even be used to connect to multiple vnc servers on a LAN behind a router with an acceptable amount of network traffic
by the way -
for the sake of security its a good idea to use ports different from the well-known ports to confuse crackers ;-)