To visit the Acropolis of Baalbeck you need to buy a ticket from the booth at the entrance of the site, before the steps that lead inside it. In December 2003 the price was of 12000 Lebanese Pounds, which is roughly 8 US dollars. It's the most expensive of the sites we visited, but also the worthiest.
Before entering the acropolis, it's best to learn something about what you will see. The easiest and most fascinating way is to visit the museum. It's located to the left of the entrance, inside what looks vaguely likes a tower/fortress. Entrance is free, and there are several informative plaques about the history and the temples of Baalbeck. There are also many of the sculptures that were originally found on the site. Simply fascinating. Entrance is free.
References to the Al Aqsa Mosque in Jerusalem are seen everywhere in the Middle East. In mural paintings, on bank notes (Jordan) or like here, a modell at the side of a road in the Beka Valley.