NPR had a story the other day about the composer Gustavo Santoalalla, the man behind the music for Brokeback Mountain. Apparently, "the music was created first and used as an inspiration for the film's shooting and for the actors." check it out - The Sound of 'Brokeback Mountain'
(note to self: stop listening to the Willie Nelson tune from the soundtrack in the morning, it's a downer. It's f*^kin' great, but it's a downer)