Teresa - I heard there is another movie of a similar genre (but about vampires), I can't remember the name of it, but it's based on a book series as well, and that is opening on the original Harry Potter day.
Apparently, this movie was set to open a few weeks after HP, but when HP moved to July 2009, this movie changed their date as well (I'm thinking it's Thanksgiving weekend?).
Anyhow....I have heard rumors that they were afraid the HP crowd would bail on HP and go to the new movie instead with them being so close together, especially since it is a brand new series and the books are bit items right now.
They may also be holding off on HP to be closer to the opening of Universal's Harry Potter themed park that is opening late 2009....
Just some other ideas....