Deathly Hallows: where will the first part end and the second begin?

The two films haven't even been released yet! However, I would think they would cut the book in half, so to speak. There might be some plot lines which go a few pages further and a few plot lines which might not be too developed, but they're making them both together because the cast is getting up there in age. Today is Daniel Radcliffe's 20th birthday! You'll be expected to believe he's still young and in school!