Now in paperback from Lisa Birnbach, the author of <i>The Offi cial Preppy Handbook, </i>comes <i>True Prep,</i> which looks at how the old guard of natural-fiber-loving, dog-worshipping, G&T-soaked preppies adapts to the new order of the Internet, cell phones, rehab, political correctness, reality TV, and . . . polar fleece.