Recently on the Playstation Blog, Seb Downie (Guerrilla Games) was asked if Killzone 2 will support custom soundtracks.

"Only for multiplayer via the XMB. In Single player the music is designed to match the action so it would be hard for us to mix up your favourite boyband."

So there we have it. At the same time as pwning noobs, you can now give your best rendition of "Barbie Girl". Beautiful