This is how I got mine...

On Audible.com they have a special offer which allows you to try them for 14 days without paying anything. They have a pretty good selection, but most importantly they have Pope Benedict's "Jesus of Nazareth" ready for download -- all you have to do is sign up.

BE WARNED: They will bill you if you don't cancel soon enough. If they do bill you, you'll find that you have *credits* which don't roll over month-to-month but allow you to get more books. Personally, I didn't think it was worth it so I canceled my subscription shortly after downloading. You do so by simply clicking on a "cancel subscription" button in your profile/preferences in you Audible account. It's simple, and they're not going to take your money if you simply unsubscribed -- i.e., it's free if you cancel within 14 days of signing up.