I think I remember reading that theres a limit of 256 people on one multiplayer game...Ill pull it up in a sec.
<EDIT> Yeah here it is:
CREATE NET GAME
This command will create a multiplayer net game. The Gamename describes the
name of the game and will be the name of the session when the game begins.
The Playername is the name you wish to give the initial host of the game. The
number of players can be between
2 and 256, and sets the maximum number of
players that can join the net game. You can optionally specify a flag which
controls the type of net game created. A value of 1 is the default and specifies a
Pier to Pier game, where a value of 2 specifies a Client/Server game. A Pier to
Pier game has every computer communicate with each other. A Client/Server
game has all player traffic routed through the host computer and then
broadcasted to the rest of the players. You will need to set a connection before
you can create a net game, however this command will automatically select the
first connection it finds if you have selected one.
SYNTAX
CREATE NET GAME Gamename, Playername, Number Of Players
CREATE NET GAME Gamename, Playername, Number Of Players, Flag