Managing Project Focus is a stand-alone class we do on the Natural Planning Model, focus and brainstorming pieces of GTD. It's also covered in day two of the Managing Workflow, Projects and Priorities class.
It's a great class, especially since it goes into so much detail on the Natural Planning Model. It's not taught as a "public" course right now, but often companies will bring it in for grads of the one-day Mastering Workflow course.
In the GTD book, the Natural Planning Model starts on page 54.