Sorry that you're having such a hard time I think yoga or pilates or something like that would probably be really good since it's non-impact, but I know you said you didn't have any tapes or instruction or anything...what about checking out a local library? Them sometimes have fitness videos you can take out?
Also, if it's a money issue (like you can't afford the shoes or tapes etc) you may want to check out FreeCycle. I don't know if you've ever heard of it but it's this neat internet thing where people give things away that they no longer need rather than try and sell them at a garage sale or just scrap them. I belong to a local FreeCycle group, and exercise stuff is often given away...shoes, books, videos, equipment...you name it. Usually someone who wanted to try something but it didn't really work out. Anyways, if you want to look into it more the website is www.freecycle.org