Far from everything...
There's a couple of steps to setting up an on-line game, and its best if both players are on the same version of DirectX, which is currently at 11 for Vista and above. This tutorial should get you going for setting up the game. It was written for a EAW title, but they all use the same interface and steps:
http://www.hist-sdc.com/help/mp.htmlThen there's the issue of firewalls. Each of you will need to make sure you have the Direct Play ports open so that traffic can pass through. How you do that depends on the firewall you have...and there's so many that I couldn't even begin to walk you through that. The ports you need to have open are:
47624 to 47624
2300 to 2400
6073 to 6073
Really my favorite way to play John's games is in a multiplayer format over a LAN, and that because firewalls and latency are not an issue. Having 3 players or so to a side is a blast, as the multiplayer module allows you to assign specific commands to people so all players on a side can move at once. Really moves the game along. The problem is finding people who can allocate the time, all at the same time...