Activating MoW on Steam

[JJMicromegas]

I purchased the game from a store but I would like to activate it on Steam so that it will automatically update. Now when I go to activate it asks me for the product code, however, I enter my CD key on the back of the manual and it tells me that it does not recognize it.

Does Steam have a separate product code for MoW that is not the CD key?

Thanks.