We have scant information concerning the System Shock 2 mutliplayer support. All we do know, is that it will be four player cooperative only. Two to four players can team up to play the single player game. The way it works, is that rather then the game being just about you, it is about you and your two to four pals, who joined up together, trained separately, and served together on the same ship, and ultimately are destined to survive the disaster together, and do battle with SHODAN and The Many, once again, together.
There will be only one player skin / model, to allow for better gameplay performance. System Shock 2 is an extremely texture rich game, and in order to improve internet play, the choice to only support one skin for the player was made.
Multiplayer in SS2 will not be included out of the box. Instead, you will have to download the patch from the LGS website. The patch will be released around the same time as the game hits store shelves.