Responding to questions we had over the Spielberg rumour (and indeed the future of the movie itself), a Microsoft spokesperson said;

We’re glad there’s still a lot of enthusiasm in the entertainment industry surrounding the idea of a Halo movie. That said, the Halo feature film remains on hold as we focus on projects like Halo 3: ODST and Halo: Reach.

Upon further questioning, Microsoft added that they had

“nothing further to share with respect to plans regarding a Halo movie”.

[Source] kotaku