I have a Linksys as well. Here is what you need to do (this will only work on your Linksys router):
Open your internet brower and type
http://192.168.1.1
This is how you access your router's setup information. You should be prompted for a password. Unless you have already changed this information, the default password is 'admin'
Once you are inside your router's setup area, slick on the tab at the far right which says 'Advanced'
Once you do this, you should be presented with a new set of tabs at the top of the page. One of these tabs should say something to the effect of 'DMZ Hosting' Note: The name of the tab may differ depending on your model.
Make sure you know to which port your computer is connected, the ports should be physically labeled on the router (1-4)
Now, click on the tab labeled 'DMZ Hosting' if you haven't already, and in the box type in '192.168.1.10x' where x is the number of the port to which your computer is connected. An example:
My computer is connected to port number 4, so I would type '192.168.1.104'
By naming your computer as the DMZ host, your computer is able to access the internet with practically no firewall restrictions. If done correctly, it will make all your ports for all your games accessible.
I hope this was of some help to you. Also, don't forget to check out the 203rd Airborne Infantry Division thread in the Squads forum.