there is a good spiritual based workout tape called woman power workout, you can get it at fatchancebellydance..
www.fcbd.com
I think it would be ok for your knees, I know it could defintly be modified, I have used alot of the moves in my dance classes and I have had many students with many different knee and ankle and all sorts of injurys and problems.
Just about anything you get can be modified in some way to fit. But I really like that tape, so I thought I would recommend it!