Network Cable/ADSL modem (NOT USB) --> hub --> PC's network card... that is all. No port forwarding necessary, a hub is not a router or even a switch...
If you want, you can even obtain multiple IP addresses from your ISP, and each PC with its own public IP address connected to the hub can play SFC online (gamespy and D2). (The cable modem can assign IP addresses to multiple machines connected to it through a hub or switch)