In an interview with Game Informer from last week, representatives from Valve confirmed that they'll be supporting DirectX 10 functionality
in the release of Half-Life 2: Episode 2
and Team Fortress 2
. This will be the case even for those folks who haven't upgraded to Vista yet. No worries if you don't have a DX10 card, though. They've got functionality nailed all the way back to DirectX 8, and are trying to push it all the way back to 7.