If Slipknot frontman Corey Taylor is nervous, he's doing his best to hide it. Decked out in full slasher-movie uniform, he dances through a doorway, belting out the chorus of Cutting Crew's "(I Just) Died in Your Arms." Some nerves could be excused: Tonight is the Iowa metal band's first-ever Madison Square Garden gig, an evening made possible, in part, by the band's 2008 Number One album, All Hope Is Gone. "I don't know why they even let us in," Taylor marvels. "They must think we're the Jonas...