Entering to the strains of "Hail to the Chief," Howard Stern considered it his due. "I'm the big star of the show. You'll see," he told a media gathering Thursday in New York, with the proceedings also piped out to interested out-of-town TV writers. The show is NBC's America's Got Talent, which launches Season 7 on Monday, May 14 with Stern replacing Piers Morgan and joining holdover judges Howie Mandel and Sharon Osbourne. Stern, 58, and now a self-described "elder statesman" of broad