bluemagic, I am usually an absolutist about reading the book before seeing the movie, but GeorgeC's post has me thinking you're right about flipping the order. He has stalled at HP 5, after zipping through the first 4, with an initial slow start, and I was using the movie as a carrot (I'm really a slow learner about intrinsic motivation!).
I'll admit usually am an absolutist about this as well. But I really couldn't be for DS and Harry Potter. He is a second child it would have been difficult to stop him from seeing the movies before he read the books. The movies were still coming out and the whole family was going when he was still a bit young to read them himself.
As to Harry Potter book 5 keep in mind it's the most tedious of the books and one of the longest. It could really use a lot of editing IMO. Harry is an angry, frustrated 15 year old and it's a hard book to get through. I myself originally gave up half way through that book and only got back into shortly before all the hoopla for book 6 came out.
There are a ton of other wonderful books out there for kids this in the 8-12 range. We had big success with checking Newbery Winners. Looking at the list I just noticed that one of the this past year's runner up's for this years Newbery El Deafo is a graphic novel.
As for reading with him the first chapters. This is something I see teachers do even in high school. Some teacher will have the class read outloud the first chapter or two and discuss them before assigning the rest of the book to read alone. Particularly with challenging material like Shakespeare.
