Are you sure it is a CD key on the case? With the UK / North American versions, the copy protection will give an error message mentioning a CD key if it fails to find the play CD (disk 2) in an optical drive, but AFAIK that is the only CD key associated with the game. The Australian version of the game uses a different copy protection, but I don't recall anyone mentioning having to enter any CD keys, so you should be fine.
