Spider-man 3 producer Grant Curtis has answered some fan questions on the official Spider-man 3 blog over at sonypictures.com where he mentions Danny Elfman's participation in the upcoming film:

Hi Grant, thanks for paying attention to us, your blog is a great idea. i had questions about the music, but i didn't know where to ask them, so i do there. Will Christopher Young use the main theme created by Danny Elfman at the beginning of the first two movies? Or will he compose a new one? Has the work on music started? Thanks, hope you'll answer me

Tim, Danny and Chris Young are both working on the picture. We have yet to start actively working on the music, but we will start soon. Thanks for the questions. Grant

Spider-Man 3 arrives in theatres on May 4, 2007.