Things get simpler if you have version 1.50.8 of the unofficial fan patch. You don't need to edit any files then.
For all players, run the Launcher GUI and select:
network -> client
connect to -> moo2.thedopefish.com
then click launch.
One of the players has to create server. In main menu click MULTI PLAYER, select NETWORK GAME, click START NEW GAME (or LOAD GAME if you are resuming an old game), choose game settings and server name (default MOX-0 might be already taken) and click accept. Tell server name to the client(s) and wait until they join.
On client(s) in main menu click MULTI PLAYER, select NETWORK GAME, click JOIN NEW GAME and select your server from the list.
When all clients have joined click START NET GAME on server
Im not sure what you mean by " chose "single player" (as stated in various forum posts we've been through),", can you explain what you call this way?