If you are talking about Windows Live Movie Maker then that is a differnet story. This tutorial is about the older version, Windows Movie Maker. And I have both of them, if you can't add music and audio at the same time then you should downgrade to this version and follow this tutorial...
@designator98 For me, I don't think it worked, I don't see -in the Computer Properties window- that my RAM has increased, it's still the same