The client must have the external IP of the computer the server is running on hardcoded into it. Your external IP can be acquired through websites dedicated to showing you your external IP, such as WhatIsMyIP.org. Open GameClient.vbp with Visual Basic 6, go to the code pane and search Current Project for "127.0.0.1" and change the value to your external IP you acquire through this website.
I tried doing this, but I could not connect to the server, and no one else could connect to it. After about a week of messing with it, I decided to try the server's internal IP in the game client instead of the external IP. That worked.
I don't know if the page is in error or if my particular set-up on my PC makes the client need the internal IP, so I haven't changed it.