If you've forgotten your username or password, simply click the link under the login boxes labeled "Forgot Your Username" or "Forgot Your Password".
If you don't remember your username, you will be sent an e-mail with your username, as long as the e-mail you submit is the one with which you subscribed to the site. If you receive an error after entering the e-mail address, simply "Create a New Account".
If you don't remember your password, you will be asked for your username (which will be verified as you enter it) and your e-mail account. This process will result in an e-mail that provides you a new password, rather than sending your existing password. Use this new password to log onto the site, then go to your profile to change your password to one you can remember!