FWIW, I picked up the February issue of Yoga Journal in the chiropractor's waiting room this afternoon, and there's an article that has probably more than you wanted to know about yoga and knees, focusing primarily on triangle pose. I only had time to skim it, but there was a lot of information about anatomy and alignment. It's not on the website - I looked - but if you're interested, it may still be on the store racks or the library.