I have a suspicion the problem is your airport ... definitely the wireless process. All wireless devices include an internal NAT firewall. I was not aware there were other brands of Airport. The timing out of you going to that test page means port 6346 is totally blocked. Have you seen this? Apple Airport Extreme/Express for Mac users * (NAT-PMP). The setting in LW Advanced>Firewalls should be set to UPnP if you use this.

Also, see OSX Firewall settings for Tiger. Though personally I keep my OSX firewall disabled. It conflicts with the firmware in my new router. And for OSX, a firewall is not really as necessary as those who use windows machines. I only use it if I am visiting 'suspect' web sites.

If your connection type to your ISP is wireless, then the firewall might be at their end.