As promised the "Free Weekend" for Day of Defeat: Source has begun (a few hours ago, sorry my connection is still screwy) and anyone can now play Day of Defeat: Source.
Simply download the Steam client. Install, create a Steam account (if you haven't previously) and you should see in "My Games" Day of Defeat: Source listed. Now simply load the game (it may take a bit) and automagically you will be able to play the game until Sunday night. You will also have access to the new Media section in Steam, which has several Day of Defeat: Source trailers, and trailers for some other games on Steam.
This comes shortly after the big "Summer Update" for Day of Defeat: Source was released about a week ago. This update included a brand new game mode called "Detonation" and two new maps for that gamemode. Along with the new maps and gamemode, several new shader effects were added along with a neat little "Film Grain" effect for when you are dead or spectating.
Enjoy the free Day of Defeat: Source weekend everyone!