"Special Bulletin," Karl/Lorimar. $59.95. Amazing: a movie-on-cassette that actually would play better with commercials. That's because this 1983 TV film, originally broadcast on NBC, takes the form of a series of TV newscasts and was structured with advertising breaks in mind. In other respects, however, the movie has lost none of its power, intensity or, unfortunately, relevancy as it deals compellingly with the issues of nuclear weapons, terrorism and the responsibility of the news media in covering terrorists--a rich, provocative mix that both honors and critiques the medium that spawned it.