There's talk about a sequel to "Who Framed Roger Rabbit," but don't look for Robert Zemeckis, who had the monumental task of directing the hit movie, to be involved. He spent some two years leading a 739-person production crew in putting together the $45 million film. "Animation is terribly hard," Zemeckis told The Philadelphia Inquirer. "One of these in a lifetime is enough." Instead, Zemeckis, who's previous credits include "Back to the Future" and "Romancing the Stone," is looking toward a "Back to the Future" sequel with Michael J. Fox. "Hey, `Back to the Future II' after all this?" he said brightly of "Roger Rabbit." "I could just phone it in."