Source: Steam
Related: Day of Defeat: Source

Day of Defeat Source is now available via Steam for the price of $19.95 USD, so people who didnt pre-order their copy, or without the Half-Life 2 Platinum package, be sure to get this and be a part of the battle as soon as possible!

There's also a small Steam update to correct a DirectX problem, which will (as always) automatically install when you restart Steam. Please do note however, DirectX 9.0c will now be required to play, and if you have an earlier version, you'll be directed here

Note: Sorry about the 1 day delay with this news, I was very sick yesterday :(