A recent convert to the discreet charms of Mexico City is the composer Michael Nyman, who bought an Art Deco home in the Colonia Roma. He divides his time between here and his native London, a city he professes to be sick of. Despite limited knowledge of Spanish, he has already arranged to do concerts, write film scores and the accompaniment to performance pieces in Mexico. Nyman wrote the music to various Peter Greenaway films, but his most well-known score is for the film The Piano, with Holly Hunter and Harvey Keitel. (The CD of that movie sold about four million copies.) Here is the maestro, resting at an antique store on Calle Campeche, from which he has decorated much of his home.