I think the first act would have to be events and relationships leading UP to the actual movie itself, and the second act would have to be the actual film- that was the biggest problem with the movie. The character development and events leading up to it were horrifically written. Not that "The Hangover" is good material in general. It made me laugh..but not much more than that.
It would be like making a musical of other horribly-written-but-otherwise-funny-because-of-the-jokes movies that also go along with the same crowd as the Hangover, (i.e. Pineapple Express, Superbad, Juno...)
Recent Broadway and Off-Broadway:: Carrie, Merrily, Ionescopade
Next On The List :: Clybourne Park, Once, Streetcar, BOM