Tee, you probably already know this, but in the forum admin area, if you go to the Forum --> Attachments and avatars --> Avatar settings, you can set the maximum width you want and leave the maximum height blank (zero). Then in the "If the avatar is too large" setting, set to "Let HTML resize it", the forum software will automatically resize the image to the width you desire, and because you did not specify the height setting, the avatar should be properly proportioned.