When asked about the effort, announced in September 2006, the Hollywood director responsible for Lord of the Rings and Dead Alive told Joystiq that the "Halo project is no longer happening, it sort of collapsed when the movie didn't end up happening."
The episodic Xbox 360 game, rumored to be titled Halo Chronicles, was to be co-developed by Jackson's Wingnut Interactive and Microsoft. Jackson's attempt at a Halo movie collapsed in 2006 just after the game project was announced, though he believed the 2007 release of Halo 3 would reignite interest in the beleaguered film. However, his Halo game was still alive in April 2008, as Microsoft was then hiring staff for it.
Its a shame
I was recently at the WETA cave in Wellington. And they were showing some reels of what they do at weta, and i noticed quite alot of stuff around Halo, they had made several Halo Body Armor's and they also had some Warthogs ripping around a track. It looked like they seriously sunk some time into it so it would be a shame if it really has been canned for good. I thought the whole thing was merely paper at the mo.
There was a youtube of the WETA guys inviting Bungie out to try the actual Warthog. I think they also worked with Neil Blomkamp on the Halo short stuff for Halo 3.