MTV Awards May Be Toned Down NEW YORK - In the 21-year history of MTV's Video Music Awards, viewers have been treated to some eye-popping moments - Prince's bare buttocks, Lil' Kim's sequined pasty, Britney and Madonna's steamy kiss last year.    But after the firestorm over the MTV-produced Super Bowl halftime show, in which Justin Timberlake ripped off part of Janet Jackson's costume to reveal her bare breast, might we see tamer VMAs when they air Sunday?    MTV President Van Toffler isn't promising any flesh-baring moments...