It looks like the original concept film is dead in the water, but there's a new effort out there to make a Halo movie... this time based on Eric Nylund's excellent
The Fall of Reach, which tells the story of how the Master Chief became Master Chief, and concludes just prior to the events at the first Halo.
More info
here, with thanks to GameDaily and Joystiq.com.
I'm on my second read-through of The Fall of Reach right now. It's really a good book and sets up the Halo Universe nicely. I really hope this movie gets made well.