For those who want to know, the 2 ports that you need to forward to host a game behind a firewall are 7597 and 17478. Give your computer a static internal ip address and go to the forwarding setting in your router and forward these 2 ports to the ip address that you give your computer. Works great for me and also allows you to stay behind the firewall without putting your computer in the DMZ, which leaves it unprotected. Additional note: I selected both tcp and udp for these ports because at the time I wasn't sure which protocol that the ports actually need to be on.
[Edited on 12-2-2002 by ruger autopsy]