I may make eventually get around to doing a full blown profile system, but in the meantime we're using gravatars for the forum avatars. that means to change your avatar from the randomly generated one, go to "http://en.gravatar.com":http://en.gravatar.com and sign up for an account. Then just add an avatar with whichever email address you used on this site, and you will have your own custom avatar.
Let me know if you have any questions.