Long before such canine upstarts as Benji and Beethoven prowled the multiplexes, there was Lassie. Much more than a dog, she was a devoted companion, a courageous protector and a fearless fighter. Lassie was a lonely boy's best friend. Indeed many baby-boomers cannot hear "Greensleeves", the indelible theme music from later episodes of her long-running TV series, without feeling an exquisite sense of nostalgia. This beloved American icon captured the hearts of millions with her sentimental but rousing adventures in a popular series of films, TV shows, a radio program, personal appearances and