Talking about Steam... as it is already confirmed in the german boards, the multiplayer and onlinelobby for SpellForce 2 FiD will be hosted by Steam. So you will have to run Steam while playing the addon, but you just have to register the game on one time online and then you can play the singleplayer and LAN-mode with Steam in offlinemode. There will be no other copyprotection besides the registration with Steam.
Vigilantus