DVD available in Discovery Channel online store
The Discovery Channel online store has a DVD listed for A Brief History of Time, but it isn't an official release. Rather it's one of those custom DVDs you can get of almost any show they have aired. The problem is that there is almost no information about the film, like whether it is widescreen or full, and no mention of Errol Morris at all. It is also listed as only 50 minutes long. So I'm not sure if this is the actual film, or just a new documentary that Discovery has done, or possibly a cut down TV version of Morris's film.
I wish somebody would release the proper version of this film on DVD.