My website is going to have a PHP image gallery (4! Images) and I also have a forum, SMF, but I want users to be able to use a common login ID that they enter in off the main site... or if they create one registration then it works for both.
Is this possible? Or more so, how would you implement this?
It is quite possible, but it will require a lot of reading and hacking to get it work. I just integrated PHPBB with coppermine (very easy to do) and a download system as well as a backend clan messaging system on a clan website I did. One login logs them into everything at once. It was not easy though.