Opening up ports in firewall

I am trying to open up a few ports in my firewall (several TCP and one UDP port) for gaming purposes. I've had people offer suggestions on how it should work, but I've never been able to get it working. Can I have someone who has done this, and is working, let me know how they got it working with some examples? :) I am using SuSE 6.4 as a Masq server to my cable modem. The other PCs on the LAN has 192.168.x.x IPs. Thanks in advance for your help. -Jesse