http://movies.nytimes.com/2007/09/21/movies/21wild.html

Directed by Sean Penn; written by Mr. Penn, based on the book by Jon Krakauer; director of photography, Eric Gautier; edited by Jay Cassidy; score by Michael Brook with songs and additional music by Eddie Vedder and Kaki King; production designer, Derek R. Hill; produced by Mr. Penn, Art Linson and Bill Pohlad; released by Paramount Vantage. Running time: 140 minutes.

From Kaki King's MySpace Page:

"Playing music for a film score. Sean Penn has written and directed a movie called Into the Wild, based on the Jon Krakauer book. I was in the studio for a few days and contributed a bunch of 'cues.' Cues are little snippets of music in a film. The experience was completely new and really challenging. I saw a screening of the entire film as it had been edited, and then spent the next two days in a studio watching scenes where they needed music. I would write a little theme, play it in real time to the scene, and then revise it until the music fit perfectly. Then I'd add some lap steel swells and other cinematic schmutz and it would be done! That movie will be released in the fall and I have got to find something to wear for the premier!!!!! Where is my personal shopper???"

There are tons of links using search words "Kaki King Into the Wild" on a thing called Google.