Ideally, you would ditch the paperback and find a hardcover version at a used book store. You MUST READ the tutorial "My Newest Book Purse" at www.craftster.org/forum/index.php?topic=140965.0;all. It is amazing - great instructions. I made a purse out a softcover book, and the key for me was: (1) reinforce the spine with a spine-sized piece of cardboard, (2) use a manila folder, cut out a piece that is just slightly smaller than the book. You will glue that to the interior of the book after you strengthen the spine. HOT TIP: A paperback or softcover book can be sewn with your sewing machine. I used mine to sew around all four sides, then tacked the side pieces in by hand.
Read that tutorial. The gal who started that thread is a mega-genius. I've made 3 book purses and she taught me a thing or two!