It's the end of an era tonight on NBC. After 20 seasons, "Law & Order" airs its final episode at 10pm. Coincidentally, one of the show's biggest and most famous fans, also makes an appearance on the series farewell. Lindsey Vonn fulfilled a lifetime dream with Olympic gold at the Vancouver games. Tonight, she lives another dream...appearing on her favorite show, "Law & Order." "The first time they said action, I was shaking really bad," recalls Vonn. That's because Vonn's been watching "Law & Order" since she was a kid, alongside her lawyer parents. But the Olympian's appearance also comes in what's turning out to be "Law & Order"'s final episode. Last week, NBC canceled its flagship drama after 456 episodes and a record tying 20 seasons. "When you got up from watching our show, you not only got a full story, you learned something too," says series star S. Epatha Merkerson. ...