You posted this question in the "knees" category, so can I assume you are concerned about arthritis specifically in the knees? If so, the movement sequence described here might help. It is quite gentle but effective.
Regarding your question about a good video for yoga for older people, I do not know personally of any. Perhaps others may have some suggestions. There is a good book out called Yoga for Arthritis by Loren Fishman and Ellen Saltonstall: I have met these people and they are good. You can learn more about them at www.sciatica.org
I checked the suggested links, they provide nice information and effective ways too.
Being a Yoga trainer, a number of my students come with this problem. The most amazing part is that, they all believe that Yoga Therapy can heal arthritis problems. I recommend them exercises and ask them to practice it continuously twice a day for at least 2 months. Most of them are satisfied.
Shalabhasana and Halasana are two forms of asanas I teach them. It's not at all tough. You need to practice them for some time though. Why don't you try these asanas?
For more information you can check these: Yoga Therapy:http://www.mothernature4u.com/yogatherapy/ Shalabhasana:http://www.mothernature4u.com/yogathera ... labhasana/ Halasana:http://www.mothernature4u.com/yogathera ... /halasana/