If you want NetMeeting to work, you need to do the following:

1. Each computer must have a direct connection to the Internet. Both you and the person you want to talk to must not be behind a firewall or "NAT" device. A NAT device allows you to connect many computers to the Internet using "private" IP addresses on your home network. These private IP addresses do not work when machines are directly connected to the Internet, but work fine when these machines are behind the NAT device. Most DSL and cable "routers" are NAT devices. If you want to use DSL or Cable, you need a DSL or Cable "modem", not router.
2. Both your ISP, and the ISP of the person that you want to talk to, must allow inbound and outbound H.323. You don't need to know the details of H.323, just ask your ISP if they allow H.323 (if you have problems).
3. You need to use the IP address to call your friend. Your friend can go to whatismyip.com and get their IP address and then email that address to you.

There are exceptions, but they introduce a lot of complexity that requires a good understanding of Windows networking. Some firewalls, like Microsoft's powerful ISA Server 2000 firewall, include an H.323 Gatekeeper that allows multiple users on your network to make NetMeeting calls.