E! Online has an article on what goes into soundtrack selection here!

“The new director, Chris Weitz, has been sending out signals that he may be open to a more experimental soundtrack than his predecessor. That could mean songs that sparkle even more than the movie’s vampires when they get caught in the sun.

“I think that might be the way it’s going,” says Marisa Baldi, West Coast partner for Zync, a music brokerage that funneled two songs onto the Twilight soundtrack. “I get the vibe that the guy is a little more into being surprised…everything is really open, and he wants to hear a lot of cool music.”