Linksys Router Configuration Help (Page 5)
Other Resources:
You're all finished! Once you have applied everything go ahead and test it out. This should also allow you to see other players while connected to a multiplayer game in DirectPlay games or if you are running the add-on module for FS2002/FS2004, FSNavigator.
Also, if you have a router setup like this, the normal "What is my IP address?" feature within multiplayer games will not give you the correct IP address for others to connect to you. Instead, it will show your local IP address from your local network. To find out what your outside (external) IP address actually is, you may use this page I have created to help you: IP Address Display Page