You can do all sorts of weight training while seated. You can use resistance bands or light weights to start with.
For cardiovascular exercise, you could try swimming if you have access to a pool. If you belong to a ymca or other health club with a pool, there are often classes specifically for people with arthritis.
Some gyms have "hand bicycles" that you pedal with your arms to raise your heartrate.
There are "chair aerobics" classes in some places. Here's an article about one I found on the net for you. Maybe you could find something similar near where you live.
http://www.thevillager.com/vil_93/getonyourbutt.html
If you are interested in a video, check the "Sit and be Fit" series, there is one specifically designed for arthritis.
http://www.collagevideo.com/cart/default.aspx
Mel