I posted this same problem in the "Have a Question?" topic, but that is frowned upon so I have to post here.
Yesterday, I installed a L4D+L4D2 bundle on Steam, and like usual it worked fine. But, when I played Garry's Mod the content for both games isn't there, and I still don't know how to get it in to the game.
Is it possible to add the L4D content into Garry's Mod without having to install it online?