OK... I have usually 3 or4 camputers on my home-network, connected o the internet, and I noticed that I can't host a GAME SERVER on the one that im using, I think its because all of the computers on my network have the SAME WAN IP! How is it possible to them to have the same IP? And how can I hos a Game erver on one of them?
You'll need to find out what port the game uses and forward that port to the computer that is hosting the game. You'll forward that port in the router. You'll need to assign the internal host computer a static IP first. 192.168.x.x. Once the static IP is assigned, you can forward the port in the router and you should be all set.