1. To start a dedicated server, you need a server .cs file, found by default in your /Starsiege folder (e.g. Server_DM_ALL.cs), which is usually referenced by a shortcut from the Start Menu.

2. You have to edit the server .cs file with a text editor to include the two lines

$TelnetPort = 29001;
$TelnetPassword = "12345"; 

The password can be anything you want it to be. Save the file, and when you start that dedicated server, telnet access will be enabled. You don't have to do anything after the game has already started.

3. Now that the server's running, you can telnet in. Go to the Windows Start Menu, choose "Run," and type in "telnet" (no quotes). Go to the "Connect" menu, and choose "Remote System." Set the host name to the IP address of your server, and change the port to "29001" (or whatever). When you connect, it should prompt you for the password you set in the server .cs file. That's it.