NEW YORK - "You get the best of both worlds," Miley Cyrus sings in the theme song of her hugely popular Disney Channel show, "Hannah Montana." It's a reference to her character's secret double life as both a rock star AND a normal schoolgirl.Offscreen, though, this 15-year-old phenom is starting to learn how hard it really is to have the best of both worlds: as a G-rated Disney superstar AND a real-life, growing teenager with an eye on a long career.Cyrus, whose fresh, easy charm and down-home southern appeal have catapulted her to an astonishing level of celebrity, especially in the past year, found herself having to apologize Sunday for some entirely un-Miley photos in Vanity Fair magazine.At a moment when she otherwise would have been relishing an amazing week — a deal for her memoirs (reportedly seven figures), the cover of People magazine and a feature in Vanity Fair — she issued a statement saying how embarassed she was. This came almost certainly at the behest of worried executives at The Walt Disney Co., for whom she will reap a reported $1 billion this year.For the record, only Cyrus' back and shoulders are bare in the most controversial shot by Annie Leibovitz, the renowned celebrity photographer. Many an Oscar-night gown would show as much skin. Cyrus herself told the magazine in an accompanying article that she found the photo, in which she gathers a sheet around her, "really artsy. It wasn't in a skanky way. And you can't say no to Annie."But Cyrus IS 15, with a fan base that begins in preschool. And it's what the photo suggests rather than shows — the idea that she might be nude, perhaps even in bed — that bothered some parents who poured their feelings onto blogs over the weekend. She wan't nude during the shoot, nor in bed, but she does have a subtle come-hither expression.Leibovitz said Monday that she and Cyrus had discussed the photos beforehand, and Vanity Fair said "Miley's parents and/or minders were on the set all day ... everyone thought i...