I have problems hosting, I can join other games, but when I try to host it just goes on pinging forever. The ports are correctly forwarded. Its frustrating, and is there any other variable(right word in english? ) that can cause this problem?

Im using Vista, and disabled the Vista firewall. But not Norton, as it for some reason is very tricky in this. I dont however get any warnings about connection "stuff". Ca nanyone help me?