I once heard a difference described between Theravada/Vipassana type practices and Zen. Vipassana is "from the inside out." Vipassana techniques are largely about what to notice, what to pay attention too, how to overcome hindrances, etc. Zen is "from the outside in" - putting mind and body dualities aside, adopting the right posture is to adopt the right state of mind.
The zazen I speak of is not learning meditation. It is simply the Dharma gate of repose and bliss, the practice-realization of totally culminated enlightenment. It is the manifestation of ultimate reality. Traps and snares can never reach it. Once its heart is grasped, you are like the dragon when he gains the water, like the tiger when she enters the mountain. For you must know that just there (in zazen) the right Dharma is manifesting itself and that, from the first, dullness and distraction are struck aside.
I was looking a a copy of of Katsuki Sekida's "Zen Training" a little while ago, which almost seems to suggest that attaining samadhi is simply a matter of getting the right posture. Interested in thoughts on this book as well.