I found this on some blog devoted to blizzard news...
A Diablo Movie
June 22nd, 2007, posted by FofR
Blizzard is hot right now, what with Starcraft 2 on its way and WoW continuing to dominate. Now we are hearing rumors of a Diablo adaptation for the big screen. These rumors came about when “Diablo” was spotted in the “In Development” section of Legendary Pictures‘ website. This notice has since been removed and Blizzard have been characteristically silent on the whole matter. Coming from an official source this is hard to classify as merely rumor, though lack of an official press statement and the notice’s removal does warrant this labelling.
Nobody really knows what’s going on at the moment - except that the Warcraft Motion Picture is still in development.
We’ll keep you tuned should any developments arise.