Michael J. Fox is trying to stub out his cigarette habit once and for all. The star of "Family Ties" has smoked as many as two packs a day but decided to give it up after the death last month of choreographer-director Bob Fosse, a notorious chain-smoker. "Granted he was 60, but I want to live a hell of a lot longer than that," Fox said. To show that he's serious, Fox enrolled in a quit-smoking program.