Here's an odd thing. The French press kit for the Halo novel Cryptum mentions a Halo movie. Involving Steven Spielberg. With vague words that it's due in 2012. That's...not far away.
You can see it at the foot of this press handout, also mentioning the involvement of Spielberg's Dreamworks studios.
But come on. This would be a Hollywood motion picture. Hollywood doesn't work like video games. You can't keep a project secret when it's being optioned, let alone in production, so there's no way such a project would be hitting theatres so quickly.
Meaning this is either complete fantasy. Or a press release using internet rumours as fact. Or simply wasn't terribly clear what was being announced, the film's release or the announcement of an announcement that the film's being made.
I'd wager it's one of the fist two, but we've contacted Microsoft, just in case it's the third.
Update: While Microsoft still hasn't responded to our request for comment, Halo mainstay Frank O'Connor did back up Luke's best guess on this, commenting on the NeoGaf forums, and I'm not making this accent up: "This is ow you say? Ah yes. Ze nonsense." I'm not sure if the funny accent is suppose to give the reaction more or less weight.
Le film Halo par Spielberg en 2012 ?! [Halo.fr]