Adam Baldwin will be voicing a non-playable character in the upcoming game Halo 3: Orbital Drop Shock Trooper for the Xbox 360 (release date is September 22, 2009).
As was the case with Halo 3, Bungie has tapped a number of vets from Joss Whedon's cult-sensation Firefly to lend their voices and likenesses to the game. As has previously been announced, Nathan Fillion, Alan Tudyk, and Adam Baldwin.
According to this
article, Adam Baldwin will voice Dutch, a member of the four-man squad that includes the game's protagonist. The other two members of this squad will be voiced by Nathan Fillion and Alan Tudyk (all three are from Firefly