The previous poster has given you some great advice. I would also recommend talking to your doctor, just to make sure they are okay with whatever exercise you want to try. Lower impact activities such as walking, swimming and biking are all easy on your joints. Here's some info from our Osteoarthritis Condition Center that I'd also suggest reading: www.sparkpeople.com/resource/health_condit
Hope that helps,
"You may have a fresh start any moment you choose, for this thing that we call "failure" is not the falling down but the staying down." Mary Pickford
"No matter how slow you go, you are still lapping everybody on the couch."