Hello. I have added wireless router to my home network and I now can not ply any games over internet. Before router only my desktop computer was connected to internet directly through cable modem. But, I had to buy a router so my sister could access internet with her laptop. I heard that I have to enable some ports but I do not know what it means. And yes, router is Linksys WRT54GL.
Enabling ports, opening ports or forwarding ports (this is correct term) is done in router configuration page and it means telling a router what ports to open for internet access. Because router acts as hardware firewall it has all ports (except most common ones) closed by default to increase network security. Go to application and gaming page of router configuration utility and add ports your games are using along with IP address of your computer. After this you will be able to play internet games just like before adding a router.