I'm trying setup portforwarding for "Steam" and Gamespy Arcade but its not working very well at all!! I play Half Life and I'm trying to create a server, but when I try to add my ip into the favourates "Not Responding" I use Zone Alarm Pro Firewall.
I had a similar prob with the same router & games - this is the work round I used.
google this - HLSW.exe - this is Half Life Server Watch, it's only a few meg. D/l it and install it (it's free) from there, you can directly enter the IP's of your fave servers to join directly. Like wise, set up your own, enter the IP and you can see from here if you're "visible" to your mates.
If your getting a "LAN class C" error, type into your console "SV_LAN 0" that should clear it up.
The process on portforward didn't work for me personally. Sometimes your ISP blocks the ports directly that Steam uses. Hope this helps