all exercise helps,so whatever you can manage to do is going to help...swimming is great as your weightless in the water and is great when you have injuries. my eldest lad as hydrotherapy and he loves it,and he doesnt feel the pain so much when hes doing that.
i have bad joints,my worst is my knee..i walk, i do wii sports games,just dance game and i have a exercise bike too.
if you wanted to use weights when doing exercise you can use small cans or large cans of beans...you could do your housework with more energy behind it too. or maybe a work out dvd. it all depends though on what you want to do with your body..
anything that makes your heart beat faster,and makes you sweat a little is good,no matter what youre trying to do