THE DROWSY CHAPERONE is a show-within-a-show. A modern-day theater addict, spending a quiet day at his Manhattan apartment, drops the needle on his recording of the 1928 musical, "The Drowsy Chaperone" and the uproariously funny musical magically bursts to life on stage. The story-line: A pampered Broadway starlet prepares to give up her career to get married while her desperate producer sets a plot in motion to sabotage the nuptials. Throw in her chaperone, the Latin lover, the debonair bridegroom, a ditzy chorus girl and two gangsters posing as pastry chefs and you've got a smash Broadway musical in any decade.