As of right now, there are going to be 4, a movie for each book in the series. But theres a rumor going around they may split Breaking Dawn into 2 movies just like Harry Potter 7... Its not definate though. :P
there is currently two. three in june. and then there will be breaking dawn. but breaking dawn is so long as you will know if you have read it, so film producers are thinking of breaking the film into two but that will be decided later