When it debuted on Broadway in 1957, West Side Story was a groundbreaking musical. A loose retelling of Shakespeare's Romeo and Juliet, the play was transported to the gritty streets of New York's upper west side and featured thuggish gangs of Italians, Irish and Puerto Ricans. It was an instant smash, as was the 1961 movie version starring Natalie Wood and Richard Beymer (which went on to win ten Academy Awards, including Best Picture). Today the Houston Symphony presents a live performance of Leonard Bernstein's sweeping and instantly recognizable score while the remastered film shows on a large screen above the orchestra. The movie's dialogue and musical performances remain unchanged; only the instrumentation has been removed. Hearing such standards as ''Maria,'' ''America'' and ''Tonight, Tonight'' on a state-of-the-art theater sound system is exciting; hearing them with a live orchestra is absolutely exhilarating.