I love the Just My Size yoga video! It was a
great beginners guide. Megan Garcia put out a book, too, and I'm just reading through it
There was nothing too strenuous about the video. Nice, fluid movements, at a fairly relaxed pace, but it's not
too easy, either. There are poses where my arms get really tired

I really do recommend it. I use it once or twice a week. (I'm actually now interested in finding a beginners yoga class in my area.)
I feel that while yoga may not be the best thing ever for weight loss (as mentioned above) that it's better to move around some than not at all. It does build a little bit of strength, and flexibility, but it really is making me feel better about my body & all that it can do.