Nvidia should be the first to host a first fully playable DirectX 10 demo called Lost Planet Extreme Edition. The demo will go live on nzone and gamesport websites at 6 PM Pacific standard time on the May 15th.
The game release date is scheduled for June 26th and this should be the first available purchasable DirectX 10 content.
Of course this is the TWIMTBP title and Nvidia throwed some series cache and the game is developer with Geforce 8 series as its reference graphic card. The game will work with DirectX 9 cards and windows XP as well.
You can find some more details here and here.