Oh, and a friendly tip: If you find out you didn't correctly set up your server's settings but don't want to have to alt-tab out of the game to bring up the server window, set an 'RCon Password' in the same tab. Simply uncheck the 'Broadcast to Master' box in the server settings and then only people on your LAN can connect to your server, i.e. If your friends ARE of the local variety, this simplifies things slightly. If you aren't adverse to strangers entering your game, though, you can leave those blank. The 'Join Password' won't stop people from connecting to your server, just joining the game, as its moniker would imply. Just click the 'Misc.' tab in the window that pops up and set a password in the 'Connect Password' box.

Contained therein are the settings for your unborn server.

Once you've downloaded and installed Zandronum, boot up Doomseeker and one of the buttons up top, I believe it's the third from the left, is the Create Server button. I would consider using Zandronum if your friends are not of the local variety, as multiplayer otherwise consists of mucking about with IPs and other things when making a server with Zandronum is just oh so much faster.

How to play brutal doom multiplayer