OK here's what you've got to do:
On "My Profile", click "Update Profile" then on "avatar image" part, click "select a different avatar image", on the URL bar on lower part, type the URL of the pic you want to use and click "Set URL" and after the photo was shown, click "select this avatar."
Oh almost forgot...if the pic is from your PC, upload it on a site.
Hope that helps <img src="/images/graemlins/wink.gif" alt="" />