Many games have been using the game engine to run their cinematics and cut scenes so this isn't anything really earth shattering. But, Bungie has tweeted
that the upcoming cinematic that you'll see on the Spike VGA awards for Halo: Reach
and I'm assuming the rest of the final game, will be run through the game's engine rather than being pre-rendered. I know a lot of people are anxious to see what's next in store for the Halo franchise and you'll get that look next week.