or is it basically about Jesus and what he has done?
Tim Keller explains how the entire Old Testament is about Jesus Christ.
One of the things I love about Keller is that he takes a high Christological approach to Old Testament studies. For a more in-depth on-line audio class on this subject, search for the "Preaching Christ in a Postmodern World" podcast in iTunes from Reformed Theological Seminary. You'll find the entire audio (35 free sessions!) of Tim Keller and Edmund Clowney teaching a D.Min. course on Christocentric preaching. Though it's a "preaching class," the concepts are applicable and essential for anyone who studies the Scriptures.