I see this available on my steam account. Is this a Beta for new features or what?

Yea, they're adding new things for Day Of Defeat: Source.

http://www.halflife2.net/2008/05/23/day-of-defeat-steamworks-update-in-beta/

"Leveraging the recently released free set of services available in Steamworks, the Day of Defeat update will add 51 achievements for DoD, player avatar display in the scoreboard and win panel, and detailed player statistics integrated with the Steam Community features (www.steamcommunity.com).

This update also adds support for popular features introduced in Valve's Team Fortress 2, the PC title named multiplayer game of the year by Gamespy.com and PC Gamer. These include "nemesis/revenge" freeze cam and new effects driven by the particle system introduced to the Source engine for TF2.

In addition, this update will also introduce a new map, dod_Palermo, which is a remix of the most popular community map, dod_salerno. Owners of Day of Defeat: Source, retail and Steam versions, may join the beta free of charge. For more information about Day of Defeat: Source or to join the beta, please visit www.steamgames.com."

Yeah it's nothing HUGE, but it's pretty sweet to see Valve adding new features to older games. I played the beta, there's really not too much different, though I did get a few achievements and felt good about that hehe.

lol, I think Day of Defeat players have had it worse than Counter-Strike players.

hopefully they'll Steamworks/achievements to other games like Counter Strike Source & Half Life 2.