Just click on your name, the click on view user profile, then click on edit profile on the top right corner, then scroll down to avatar type, select specify a remote image, then upload any picture you want. I put my pics on www.photobucket.com and then just copy the link to it. The pic has to be between 1 and 100 pixels though. Let me know if you have any problems.
Did you register an account? When you have uploaded your picture, do you copy and paste the URL link of the pic when you click on the IMG button to post the pic here? If that's not it, how is photobucket not working?