I am trying to setup a Return to Castle Wolfenstein: Enemy Territory deticated game server over the internet. I am behind a LinkSys WRT54GS wireless router. I have all the ports for the game on forward. The server is not ment to be over LAN its ment to run over the internet so anyone can join yet when I run it the IP appears as the default 192.168.1.100 and that obviously isnt my WAN (internet) IP. I also had a friend try and join on his own computer and internet connection and he couldnt. Is there a way so I can host the server behind the router and have people beable to join by typing in my WAN IP? I am running the server on Slackware Linux but I am almost positive that wouldnt affect this.

It is perfectly normal and OK that you connect with the internal IP - afterall, you are connected from your internal network and not from the Internet. That is not a problem.
However, your friend should be able to connect if you have setup the IP forwarding correctly. Try looking into the logs of the router, maybe packages get rejected? Maybe there is another port that you need to open?

Maybe it shows my lack of imagination but I don't see how it's possible. You can't use 192.168.1.100 as your address out on the internet as numbers that start 192.168 are reserved for use on local area networks. Your router will have been given a unique IP address when you dialed up your ISP but you can't use that because the router isn't the server, it wouldn't know what to do with the packets. If you were using a linux PC as the gateway it may be possible to filter the packets with some clever iptables rule so that they were forwarded to the right machine, but you're asking a lot of a wireless router