i know the song that is the acoustic guitar in the midtrailer...it is Beck - Lost Cause
There are 3 pieces of music in the Tarnation trailer... the 1st is an outtake from the film's "orchestral" score by the composer John Califra. The middle piece, named appropriately enough "Tarnation", is one of the film's original instrumental tracks written by Tin Drum producer Max Avery Lichtenstein. The 3rd and final piece is a song called "Safe As Milk" that Max produced with the band Hopewell for their 2001 record "The Curved Glass". You can download the latter 2 files from a special Tarnation section of the Tin Drum Recordings website (http://www.tindrum.com/tarnation)... thanks for listening!

- Tin Drum Recordings