The fox isn't the best choice to guard the chickens-and The Tobacco Institute isn't the ideal choice to convince kids they shouldn't smoke, says Dr. Joseph R. DiFranza of the University of Massachusetts Medical School. One of its programs, "Tobacco: Helping Youth Say No," actually encourages smoking, he charges, by portraying it as a "forbidden" adult activity-and failing to acknowledge that it's addictive and potentially lethal. The institute says DiFranza misrepresents its goalsTECHNOLOGY