can't host games WarcraftIII

My son is running WindowsXP SP-2 and has his Window's Firewall off. He can play online games but cannot "host" games on WarcraftIII, but he is able to host games such as Age of Empires & Diablo. He is running through a Microsoft router (Model MN500) through a cable modem. His online friend told him to open the router port & change it from 6112 to 6119. We have no idea how to do this. Does anyone have any suggestions about how we can help him be able to host games with WarcraftIII? Thank you in advance! Chuck

 

http://www.portforward.com/microsoft/mn-500.htm

that link should be of some use to you (I think),

all the best,

-Ciz