Establishing A Netmeeting connection

I’ve already installed ILS Server in a Windows NT Server 4.0. But however the communication can only be established in Local Area Network. I can see all the user name in the directory but could not communicate with them if they are outside the rangeof our Local Area Network. My Server was behind a router and a firewall.

1.) What is the necessary configuration should I make in my server?

2.) What the user need to configure?