Hi Barnes,
Have you thought of taking a 6-8 week course in yoga? I've been using yoga for exercise for several years now, and I started off by taking a short course in it. It is possible to teach yourself but I found during the course that I had picked up some bad habits and wasn't doing some of the positions properly. The teacher pointed these out and corrected me, and her advice and training has benefited me when doing yoga at home.
I've found Ashtanga Yoga by David Swenson (book) to be a great guide throughout the years. It's a ring bound book that sits flat on the floor, and explains each position in depth. I don't currently own a yoga DVD, but I've found user's reviews on Amazon very useful in the past.
Best of luck!