amazinly good link for this: http://www.createforum.com/wc3cg/viewtopic.php?t=534&mforum=wc3cg
I'm one of the forum users there. It's a custom game called "cardcraft"'s forums.

Another place to try is portforward.com, try the link and click on the connection you use, if it isn't there then try one of them, for the information is pretty generic.
http://www.portforward.com/english/applications/port_forwarding/Warcraft_III/Warcraft_IIIindex.htm

If you continue to have problems, pm me. Some programs can be designed to open ports even if they weren't meant to do that.
Solved my hosting on 3 different networks on 3 different computers (although none of which were mac's though, i still expect i could google answers to questions anyway).