Now that I've asked the question, I'm trying to think of Act breaks for ANH.

Act 1 ends when Luke goes to bed the night he gets the droids? This is before Obi-Wan and Han have been introduced... so I'm tempted to say it can't be then. By that logic, it seems that the break has to be after they leave Tatooine? All of the Characters are introduced and it seems that it's a short trip to Alderaan to end Luke's story. Obviously that won't help Princess Leia much...

Act 2 would then contain the destruction of Alderaan, the capture of the Millennium Falcon and all aboard, the rescue of Leia and the near death of almost all in the trash compactor, and ends, more or less with the death of Ben.

Not sure if the TIE attack is the end of 2 or the start of 3.

Act 3 is pretty short. But it involves the threat of the Death Star taking out the whole Rebellion and the battle at the end leading to the ultimate conclusion.

Does that sound about right?

One of the amazing things about the first movie to me, which I elaborated on here a bit, http://originaltrilogy.com/forum/topic.cfm/A-New-Hope-Trading-on-Promises-or-Trailer-for-the-SW-Universe/topic/11379/ , is that ANH introduces the SW galaxy and conflict at large, but the narrative of the movie somehow convincingly focuses on the threat of the Death Star... so that when the movie ends and the only real resolution it offers is that the DS threat has been conquered... It's really an excellent example, and perhaps the definition, of a movie having the 3 Act structure internally while also serving as a macro Act 1 in a trilogy. It's really quite well done.