The Last Impresario--the most famous person you've never heard of--is now the subject of a major motion picture, directed by Gracie Otto.   Michael White is one of the most inspirational producers of our time, responsible for changing the face of Britain's cultural scene in the 1970s. White has been involved in an amazingly wide range of shows, many of them hits, some of them disastrous failures, all of them unusual. His career encompasses the plays of Athol Fugard, Joe Orton's Loot, Oh! Calcutta!, the catastrophic Jeeves, the money-spinning Sleuth, The Threepenny Opera, starring Vanessa Redgrave, The Rocky Horror Show, and movies ranging from My Dinner with Andre to Monty Python cannot, by the wildest stretch of the imagination, be dubbed conventional.    In this autobiography, originally published as Empty Seats in 1984, Michael White tells many marvelous stories and asks some wonderful questions. Why did Orson Welles make a one-armed Peter Daubeny carry his suitcases? What really happened during a performance of The Dirtiest Show in Town? What did Peter Sellers do to Spike Milligan's roast chicken? What were Kenneth Tynan, Joe Orton, and Dame Edna Everage really like? The reader discovers how a play is put on, what kind of money is involved, what techniques are used. "You, too," White seems to say, "can be a producer. And this is how you set about it." Drawing on all too many experiences he might prefer to forget, White would no doubt add, "And that way madness lies."