It's a great introduction to Pilates and well worth the cost. It strengthens your tummy, legs, backside, back, arms. It's made my legs leaner and I just feel more flexible all-around.
All the above DVDs are fine for beginners (esp. Dummies and Windsor), and also allow for growth within the video. You work at your own pace. I strongly recommend it.
I do both Pilates and Yoga (Yoga Conditioning for Weight Loss, Crunch! Yoga) regularly and not only do they both help me stay in shape, they help my IBS tremendously.