This is the new Open Air Summer Cinema, just along from the Oceanographic Museum. It advertises as starting at 9.45 at night but normally it's 10 p.m. or later. You can buy a glass of wine, you can sit in lounges or chairs. The films are in English with French subtitles - and it's a great place to meet up with friends. Why not come tomorrow - they are showing Harry Potter and the Order of the Phoenix? It's rather magical setting I think you'll agree. Click on the website of the Summer Cinema, scroll down, and you'll see a map of exactly where this is on the Rock.
Official Website: http://www.cinemasporting.com/
(from the Monte Carlo Daily Photo blog: http://monte-carlo-daily-photo.blogspot.com/2007/07/monaco-open-air-cinema.html)