I believe Linksys routers should understand UPnP technology. So your Tools>Options>Advanced>Firewalls should be set to UPnP without the need for port forwarding. (Perhaps you could try a different listening port for each computer. Just a thought.)

However, if there is a problem & forwarding a port seems the only solutions then there's 3 steps you need to follow:

1. Set up a Static IP. Setting up a Static IP for Linksys

2. Forward a port (Port 6346) Forward a port on a Linksys

3. Force IP within LW: Force IP instructions & sample image & 2 posts after that.

* Note you can only forward one port per app per computer. If you were to run LW on the other computers then you'd need to use another port no. for each (eg: port 6344, 6342, etc.)

* It is extremely important that you MUST have a static ip for port forwarding to work. Otherwise it won't work the next time you log on.