The Multiplayer key for this game functions as the in-game CD key as well. Some older titles have this functionality and adapting them for online activation wasn't as smooth as with newer Games
Enter your multiplayer key ( you can access this by logging into your Direct2Drive account and checking your Key button next to your game's box art ) to proceed to profile creation for your game.
There is no Copy/Paste functionality when in-game, so its best to write the key down and then enter it so you don't have to alt-tab. Sorry about that!