To setup Port Forwarding on the WHR router, you must first log into the router ( http://192.168.11.1). One you are logged in, click on "Internet Games (Port Mapping)".Here you can enter the UDP ports, and TCP ports, as well as the IPaddress to forward the port to. If you need to enter multiple ports foreither TCP or UDP, you can use a hyphen (-) to denote a range on ports.So, if you need to forward all ports from 8000 to 8100 you can under8000-8100.
Also if it is asking for a username and password try the default login of root with no password