In that case it should be fairly easy to do - The only thing that you may need to watch out (I've never attempted this myself with vB 3.5 or 3.6 ) for is how the password is stored in vBulletin, as it uses an md5 hash with a unique salt; Looking through how the registration file does it should tell you how that is created but if there are any questions, you are likely to find someone who knows here