Here is a game (supreme commander) using your router
http://www.portforward.com/english/routers/port_forwarding/Belkin/F5D7231-4/Supreme_Commander.htm
You see where it says "We will list a series of lines here that will show you exactly how to forward the ports you need to forward. Supreme Commander requires you to forward the 6112,9103,30350-30351 ports. Go ahead and enter the settings shown above into the Virtual servers menu."
The ports for Demigod is 6073, 6100-6200 instead of "6112,9103,30350-30351"
Then try following those instructions on how to set it.