A once-promising experiment to see if treating genital herpes with a common drug could dramatically reduce susceptibility to HIV infection has found no protection whatsoever -- a shocking setback for researchers hoping to find a pill that would slow the spread of the AIDS epidemic. Results of the long-awaited study, which included gay men in San Francisco, Seattle, New York and Peru, as well as women in Africa, were released here Monday at the 15th annual Retrovirus conference, the premiere annual scientific meeting of AIDS researchers.