AMFAR Hip New Yorkers descend on Central Park for the 11th annual benefit, "Boathouse Rocks the Tavern, " but the hippest one may be the singer Sasha Lazard, who will perform several songs from her album "The Myth of Red." Equally at home at the Metropol itan Opera house- and Parisian dance clubs, Ms. Lazard has created a new genre of music called trance opera, in which arias and fast electronic beats form beautiful cinematic music. Proceeds will benefit the American Foun dation for AIDS Research. Monday, 8 p.m.-12 a.m., Tavern on the Green, Central Park West at West 67th Street, 212-806-1636, $100 and up. Party attire.