NOTE: The management of user accounts is now handled centrally on the site, so you only have to register once and you have access to all areas, including the forums and the premium area for AiGameDev.com Insiders.
If you originally signed up to the forums, you'll need to request your password first, then activate your Insider account once by visiting this page. If you have any trouble, contact <support at AiGameDev.com> by email.