ET has the details... Madonna , Sting , Janet Jackson : Just a few of the big names who've performed at the MTV Music Video Awards. And now, the Jonas Brothers get ready to join that elite list. ET was on hand for a press conference Friday as the pop trio announced they'll flex their musical muscles at the annual awards show, set to air live September 7 at 9 p.m. Though the brothers didn't reveal what irresistibly catchy tune in their back catalog they'd play, they did divulge that the song would involve fan interaction. Then, after bopping through a cover of Shania Twain 's "I'm Gonna Get You," they revealed that Joe graduated high school this week! ...