The first movie will be all of "The Hobbit", telling all of the travels of Bilbo and the dwarves and such. No more to say here, other than that it's going to be AWESOME.
The second movie will not be based on something J.R.R. Tolkein wrote; it will be about the 60 years in between the Hobbit and FotR. I'm not sure what about, though - it could be about The Shire in that period of time, or perhaps more expanding of the Istari, or maybe even Gandalf's, Aragorn's, and the White Council's hunt for Gollum.