Ok. For one, NetMeeting is no longer direct connect. Microsoft has totally screwed up Netmeeting AND MSN Messenger. If you use MSN Messenger you're going to notice that, no matter how many ports you opened, you can't do voice or video on msn messenger.
NetMeeting and MSN Messenger can only run on what is referred to as Universal Plug and Play NAT. Basic NAT says that any traffic coming from this designated port, goes to this location. Now, NetMeeting uses Plug and Play NAT. The program switches from port to port as it feels necessary. And seeing as you don't know which port in the 65,000+ ports available to you it's using, normal NAT is worthless.
SO, yes, it's not working because of NAT, kinda. Your router doesn't support Universal Plug and Play NAT. Most cheap broadband aimed routers don't. If it don't say Cisco on it, it doesn't support UPnP NAT.
Forwarding one port isn't going to solve the problem. You will be able to do voice and file transfers only. You won't be able to do voice and video.
About the only thing that you can do to get around this, is to get a router that will let you designate a DMZ computer. That is the only way you'll get these types of programs working.
Microsoft really blew it on this as far as I'm concerned, and AFAIK, have no intention of correcting this issue. Yahoo Messenger will work fine behind a router for voice and video if you open the proper ports (only 2), and there are other programs that don't do this port hopping. But Microsoft uses it. There is also another stigmata about the UPnP NAT. Only one machine can have it. If both routers do UPnP NAT, for some reason.
Gotta love Microsoft