It's impossible to resist the comparisons--Tchaikovsky and Marius Petipa in the waning years of the 19th century; Igor Stravinsky and George Balanchine in the middle decades of the 20th. These relationships between important composers and major choreographers were so fertile that they rewrote the history of artistic collaboration. Now, as dance limps uncertainly toward the millennium, Lou Harrison and Mark Morris look like the latest team to fuse sound and step posterity as they ...