Most routers have the option to configure with a web browser. For example, my Linksys router's configuration page can be accessed with
http://192.168.1.1. This is probably the same for yours. If not, your router's IP can be seen in the TCP/IP control panel (mac or pc) as gateway, router, etc.
Now, you will want to check out the manual for the bastard here:
http://www.sohoware.com/serv/downloads.htm.
I'm guessing you have the BroadGuard Router - NBG800(it's the only router there). In the manual, there are sections that explain about DMZ and port fowarding... READ THEM OR DIE!!
Which port(s) to foward if you choose NOT to use DMZ?
Here's a list for all of the GR-hosted game ports:
http://gameranger.com/help/ports/. If you need PC game ports... well too fucking bad.
Hope this helps... beyotch.