I read that book recently. My favorite part was when they were about to come up with some incredible breakthrough in their quest, and then the police came and they had to make an amazingly improbable escape. Edit to add: I don't think Tom Hanks would be very good for the main character. I could see Nicholas Cage in a Jerry Bruckheimer production though. Oh, wait, that movie is coming out in a few weeks, it's called "National Treasure."
Hanks is bookish enough, perhaps, but it seems like one of those roles that would have gone to Harrison Ford if it were 8-10 years ago. With the success of both books, I'm a bit surprised that they aren't shooting Angles & Demons first, but maybe they will do that second and pretend it comes after.
Angels and Demons was the better book in my mind. But it wasn't nearly as popular as DaVinci. It will be the sucky prequel that gets rushed out if the DaVinci film does well. Shame, it would be the better movie.