Jonah Levin knows what it's like to sit atop the world of pop music. But chart-topping hits (as well as enduring marriages) are harder to come by ' and nothing he ever knew could prepare him for the skid to the bottom. Playing Jonah, the enduringly talented Paul Simon knows the musical terrain ' but scores in acting and screenwriting areas as well in this sometimes funny, always probing look at the intriguing starmaking machinery of the recording industry. Blair Brown, Rip Torn, Joan Hackett and Lou Reed also score among the movie's performances. Among the 10 soundtrack Simon songs are Ace in the Hole, Late in the Evening, the title tune and That's Why God Made the Movies. Offering a showcase to a master musician like Simon is another divine reason to carry this cinematic tune.