A mainstay of New York theater since the early 1980s, the openly gay Paul Rudnick has become a latter-day Dorothy Parker, animating plays, screenplays, novels and a column in PREMIERE magazine (under the pseudonym Libby Gelman-Waxner) with his subversive wit. Soon after graduating from Yale, his off-Broadway debut, "Poor Little Lambs" (1982, starring Kevin Bacon and Bronson Pinchot), received mixed notices but attracted Hollywood attention, although ultimately languishing in developmental limbo before the rights reverted to Rudnick. The former book jacket blurb writer took a break from