Public domain movie resources

[MisterGrey]

A FOAF owns and runs a small coffee shop, and as a "community event" wanted to start having free movie screenings on Friday nights. He'd originally planned to simply get movies from his own home library or Hollywood video, thinking that because the screenings would be free he'd be OK, but I explained to him that this would still constitute copyright violation and told him that he should look into getting his hands on some public domain films. He's asked me to help him out, but I've run into the snag that conflicting websites list conflicting films as having lapsed into the public domain; and for more recent films, there's no explanation as to how they ended up in the PD, if they are in fact there (such as the omission of a copyright notice in the 60s/70s). I've also run into the snag that, for some films apparently in the PD, individual distributors have copyrighted their "version" of the film, preventing me from finding out for certain if it's PD or not (for example, the original "Night of the Living Dead," definitely in the PD, has several dozen entries in the online copyright records, but for video copies and not for the film itself). Again, some dollar DVD movies, for example, I've found to be in the PD, but they also pop up on copyright searches for the numerous distributors.

I want to help this guy out and part of that is making sure he doesn't face any legal repercussions. Anyone have any helpful information for determining PD status on movies?