As my past posts show, I used to really be against yoga. Before converting to Eastern Orthodoxy, I took yoga for awhile and was exposed to a lot of Hinduism. At the time, I was open to those teachings and really enjoyed them. After having talked to some folks (both on this forum and outside), I came to the conclusion that yoga without
the spirituality can most definitely be beneficial. I have a few yoga videos (all with Rodney Yee) and have enjoyed them over the years. I also have two very helpful books on yoga. Both are helpful, but if there's any way you can swing it (maybe your school offers it? Also, yoga studios offer discounts to students...), you really need the help of a professional teacher. They will be able to monitor your posture and make corrections (something really difficult to do on your own). They'll also be able to answer questions you're sure to have about the various postures.
Good luck! It's bigtime fun and beneficial if you get the right instructor.