There is a lot of information on the Halo movie
here, at the Wiki site. The long and short of it is that the movie was in the works, with Peter Jackson and Fran Walsh set to produce it, Neill Blomkamp to direct it, and WETA Workshop ready to do the FX work for it, when the studios decided to pull the plug on financing it. Something to do with their shortsightedness and complete misunderstanding of how much money they could make on "just another video game" property.
So, what you see in those video shorts are basically all that remain of that project. Neill Blomkamp directed those and all the props and effects (including the full size, working Warthog vehicle) were ready to go. Given that Halo 3 is making so much money, expect to see the movie studios change their minds, although Blomkamp is now saying that he doubts he will be involved with it and that the movie would be different than what they originally planned. Jackson loves the game and the story and would still do it.
My brother works at a Sony Style store in King of Prussia, Pennsylvania (just outside of Philadelphia) and who other than Peter Jackson himself walked into their store. A couple of other employees asked him about the status of the Halo movie and he said that he thinks it will be back on track.