Hi there,
If you're having trouble seeing other people's servers, then one of two things is happening. Either 1) there are no servers at the time you are looking, which doesn't sound like it's the case since you're in the channel with other folks -- so long as they advertised their server, or 2) some sort of firewall is blocking outgoing requests from AVWW.
Port forwarding and router settings really shouldn't be involved until you are actually trying to connect to someone's server. And even there, you should have to make no changes unless they are trying to connect to you.
When I say "firewall" above, what I really mean is "software firewall." Are you able to see beta updates of the game when you start the game? If not, then that too is being blocked by a software firewall. Something like zone alarm, windows firewall, the firewall in the Norton software, or various others.
If you make an exception for AVWW in any software firewall(s) you have, then you should be able to see the server listings and the beta updates. After that point, assuming that the other person has their server set up correctly, you should be able to connect to them.
The fact that it doesn't even work over Tunngle makes it even more likely that this is a software firewall. However, it's possible that searching on the LAN on Tunngle might not actually find results in general. If you know who has the server up on the Tunngle list, then entering their Tunngle IP for a direct connection is a better way to test that. Finding LAN games involves sending a kind of broadcast packet over the local network which some of the VPN services don't pass along; I'm not sure about Tunngle.
By the way, be careful with the DMZ settings on your router -- you probably want to turn that back off to avoid having any problems with malicious intrusions into your network from outside.
Hope that helps!