If you have registered on the site but are having difficulty staying logged in (i.e. you login, go into a board and it says you are no longer logged in) you will need to clear your browsers cookie files. This issue is caused by an old/outdated cookie file overriding the more current one.
If you have forgotten your username or password, you can request to have your username emailed to you and to reset your password. When you fill in your registered email address, you will be sent instructions on how to reset your password.