Well we got contact with the some of the programmers from the original team. These guys were around here at the release of the game and helped us.
The right on the source code lie at Activision, an EULA comes with the source code, that's something else then a GNU GPL. So if you want to sell something based on the source code you have to asked Activision. That's different in comparision to the Anet code as there they can hope that others have to maintain a server for their games, if they want to use it for their games.