Routing / port forwading ip video calls – Cisco 871(w)

Hello all, Pease, please help. I am trying to set up my Cisco 871(w) to route/port forward incomming video calls to a polycom Viewstation video conference unit. Obviously I have tested the unit when connected directly to my cable modem and works with no problems. I can call out through the router but untill it is et up it will not know where to forward an incoming call to. Can anyone send a config that I can enter into the router that will solve my problem please. The 871w is currently set up as a standard DHCP Home router.Lets say that the video unit is in port 2. I have completed ccna so command line entry is not a problem.

Appreciate any help.

Thank you

John