If you forget your username or password, just click the "Login" link at the top, then under the login box click the "I forgot my password" link. Just input in your email address, and your username and temporary new password will be emailed to you. If you remember your username/password and used the forgot password tool, you can just ignore the email you receive - your password won't be reset to the temporary password until you click the new password activation link in the email (it says this in the email too).
Some notes: you can use the same username / password or register different ones for the message boards / gym listings & ratings / classifieds - the registration username and password for the gymnast webs and club teams web is separate, but you can try to register the same username as your web at the message boards/listings/classifieds if you would like.
:D