I was curious too, especially about the music in the latter part of the trailer . I think this page answers the question:
http://www.soundtrack.net/trailers/?cid=N&id=1435

> what soundtrack is the music from the Notebook movie trailer form..? the part from the very beginning of the trailer - where you see the kids ridding their bikes..? it starts with a simple piano part..then goes into really pretty stuff..WHATS IT FFROM!?!? omg i have to know..haha. it's driving me crazy.