Keith,
A lot of what I've found ('muscle energy technique' on google) has been very superficial or technical (my vocab for this type thing isn't that great, yet, so am looking for something basic), but the following powerpoint file seems to hit a lot of the high points, including a little of how it works, although I haven't digested it yet.
www.ohwi.org/Presentations/ Introduction%20to%20Muscle%20Energy%20Technique1.ppt
I also found a book on amazon (also available elsewhere) Muscle Energy Techniques by Leon Chaitow that looks like it might be useful ($62.95, but cheaper some other places). It comes with a CD. Reviews suggest it might be useful for novices.
I agree with Brewerbry that it is probably difficult to do the 'self energy muscle techniques' at home that the PT showed me. That is, I can do them, but probably not with the same results that the PT did since he is more knowledgeable about the feel. I wished I hadn't been tied up in the field or at events the 2.5 days after my appointment so I could have started the exercises while the feel was fresh in my mind.