I love yoga. There are lots of books about it, and some websites, and even magazines. I've learned a lot from working with video. I would really like to go to a yoga class sometime, but haven't yet. I think that the live class experience would be really neat. I guess I don't know enough about yoga to give you much by way of answers, but I would suggest finding a teacher, or at least some good videos.

Yes, there is spirituality involved in yoga, but it is a choice how you want to focus. A lot of people really do it for exercise. Maybe that opens a door to spirituality, but yoga isn't about replacing anyone's belief system. Yoga is an 8-limbic tree. The limbs include physical aspects such as postures and breathing, as well as meditation and philosophy:
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Yama - Moral observances for interactions with others
Niyama - Moral observances for interactions with yourself
Asana - Postures
Pranayama - Breathing
Pratyahara - Sensory inhibition
Dharana - Focus
Dhyana - Meditation
Samadhi - Blissful absorption of one's individual consciousness in the essence of God.
http://yoga.iloveindia.com/limbs-of-yoga/index.html

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There are also various kinds of yoga. Some focus more on certain limbs than others.