D&D Movies
While I don't remember any being people sitting around playing seriously, when WOTC did that competition of D&D video clips, there were several that captured the feel of game play quite nicely. At least one was just someone moving miniatures around on the screen, but it was believable as session. You may be able to find something there -- assuming they're still on the web.
However, I have to agree with a number of other posters that a typical D&D game would be boring to an outsider. Now, if you had some time and skill, you could edit the recording of the game down to the most interesting bits and then switch to an animation of what their characters were doing. (The "imagination view", as it were.) What you'd have would be an awful lot like "The Gamers". (Which while being an blast of a movie, wasn't all that serious.)
The truth is, I don't think most of us just don't take the hobby serious enough to produce an actual "serious" movie about a gaming session. People are going to go for the laugh. (Heck, they go for the laugh IN my game, why wouldn't they do it in a movie about the game?)
Of course, I could be wrong. I would never have believed that millions of people would watch poker on TV.