You'd be better off with a book. Something that doesn't require electricity and you can carry it around with you in the great outdoors. Make the mind silent. Practice practice practice. See the meditation, having problems thread. Post #5 There, I've just saved you a bunch of money. x
If you have a good internet connect then check out Yoga Today http://www.yogatoday.com/ I have not watched many of them but what I have seen and done were pretty good.
If you have satilite or digital cable you should have the FitTV chanel. They have a yoga series called namaste. I tivo them so I can do them in sequence. Each one is 20 minutes (after skipping the commericals). The sequence is good for all levels. I stay in downward dog during the last pose in each sequence because I aqm a bit out of shape and can no longer do the more advanced poses, thus it's great for all levels.
Yoga dvds are nice but you should really find a teacher. They can assist you in correct positioning of the body. Yoga originaly was meant to be taaught individually and studied for years. You might be cutting yourself short if you do not get that one on one help. Also, you could hurt yourself. I did videos for the longest time and I thought I was pretty good, than I went to a class and realized I was doign them wrong! I had to start over again. Not that I am complaining of course. I just hope you can try a class first, get an idea of how to move into and through the poses and then maybe try a video. Namaste.