Okay, I'll help you out. I have a linksys as well. I'm not very good at it yet (I still can't say, host a dedicated server on one comp and hop on through the other online, but I got it to work for listen servers).
There is a tab on the router setup page (for mine, it's like
http://192.168.1.1 or something to that effect) called "Advanced." Once you click that, you will find an area for "Port Forwarding." Find out what the IP address of the computer you want to host on is, and fill in the range of ports to have forwarded and that computer's IP. Check off both UDP and TCP or whatever the second option is (it's different for you I think).
The port range I use is 27005 - 27015, I think. That handles at least the listen server and connecting. If you assign at least that range to the PC you want to host on, it should work.
Just remember, I can't get dedicated to work. I'm still working on that problem...I'll keep you posted, though.
Hope I helped.