Fresh from his triumph as a gay cowboy in Brokeback Mountain, Heath Ledger re-ups as a hetero playing the world’s greatest eighteenth-century lover. His comic flair is a big plus in a film that is fanatically busy and fatally sexless. The whimsical plot, involving Casanova’s seduction of a cross-dressing feminist (Sienna Miller rivals the Venice locale for beauty), isn’t helped by director Lasse Hallstrom’s leaden hand. Oliver Platt is fun as the “lard king” with a yen for Miller, but he’s just pineapple to the ham of Jeremy Irons as a bishop out to kill all erotic thoughts. No sweat. The movie does it for him.