I felt most comfortable starting with some videos at home before I took a class. I used this video and loved it:
http://www.amazon.com/Yoga-Just-Size-Megan-Garcia/dp/B0006TPDXO/ref=sr_1_1?ie=UTF8&qid=1321976369&sr=8-1 When I started classes, I felt so much more confident at least having become comfortable with the basic moves. I still do the video when I can't make it to a class or want some extra movement.