Answer: That’s right, you split said book into two movies!
Twilight New Moon is smashing records all over the place because it’s fan base are that of young teenagers (and my wife!) who will go and see Robert Pattinson and Taylor Lautner (and Krsiten Stewart?!) take their shirt off as many times as Summit can fit into a movie. News is leaking today that Summit Entertainment are considering turning Breaking Dawn, the fourth installment of the Twilight Series into two parts, much like that of the final Harry Potter book, Harry Potter and the Deathly Hallows. New Moon has currently made around $481m worldwide and it’s only been out two weeks! Can you blame Summit for trying to extend this success as long as possible? I sure can’t.
Variety have the full info which you can check out here.
While I think any movie studio would milk this franchise for as much as possible, I also believe that BD has so much to it that it almost has to be two movies.
As far as the age group this appeals to, while it does target teens/tweens don't underestimate the appeal to the over 18 and beyond group. I know many very grown, married-with-children women that are completely absorbed with the stories, movies, etc.
The difference between splitting this book up and the final Harry Potter book up is the Twighlight books are so terribly written. Anyone who isn't a die hard fan will tell you that. There isn't enough to break it up. The dang movies are already so slow….the constant stalker staring in the first one was unbearable. So I guess they will go back to that to fill time. wildchild is right that there are some adult women obsessed with Twilight….pretty sad.