Internet TCP/IP Connection
The best method of multiplayer I have found is using Internet TCP/IP Connection in H&D. Here there are pictorial instructions on how to setup and use TCP/IP multiplayer in H&D and how one can avoid many of the bugs involved.

Player ICQ Contact Listings
One of the best methods of finding fellow H&D players is by using the cool little chat program ICQ (meaning "I-seek-you") and adding contacts via player listings such as this one. It is a awesome little program, I use it for all my type-chatting. (Updates Automatically)

Roger Wilco Voice Chat
The cool program Roger Wilco is recommended by the game developers for voice chat during H&D gameplay. It is the coolest little (under half a megabyte!) dual-duplex voice chat program, with the exception of the small lag on 56K connections, it is totally awesome for coordinating maneuvers in H&D.