It's not easy to take over for a guy like Allen Darnel, a 55-year ballroom-dance veteran who taught celebrities such as Zsa Zsa Gabor and Aldous Huxley. But now W. Michael Smith and Enrique Baez-Trevino are cutting in on the recently retired Beginners Only Social Ballroom & Latin Dance Studio founder's waltz, and they have impressive resumés of their own to brandish. Baez-Trevino has studied under prominent trainers since he was 13, and Smith has trained in both theater and broadcasting, a background he believes helps him give clear instructions to his students. These two masters lead 45-minute private lessons for individuals, couples, and groups of eight or fewer, sharing their knowledge of swing, salsa, and the tango in private rooms. The schedule is unusually flexible, with lessons available seven days a week all the way until 10 p.m.