Forwarding ports/opening ports/what the heck?

Ok i am in a dilemma. Although I am knowledgable about computer hard/software as a whole, I know absolutely nothing about networking, routers, etc.

Now, here's my problem.

I play a game called Altitude at www.gamedit.com/~lampster (I'm Skywalker). I want to know how to set up my own server to play. It's not acutally a server, more like a pseudo-server. The problem is that my server gets up but it can't communicate with other computers i think. If that confuses you scroll down to the next paragraph.

Ok, I have traced the problem to needing to forward or open up the ports on my router. How do you do this? By ports I mean like port 28020, port 33464, etc. How do you open up or forward a port on your router? I have a Linksys wireless router. Also, don't tell me it's my firewall becauase I already shut it off.