I got mine from
www.animationfactory.com. It's a cool site because they allow you to edit the pictures right on their site. I had to make it small enough (got a message that the pic couldn't be larger than 50x50) in order to be able to use it. They have tons of cool animated graphics.
Once you have the picture saved on your hard drive, just use the custom feature for the avatars. It allows you to browse to the file and add it.