I have a main site with it's own user database and registration system, what I want is to create some sort of relation between this user database and a WordPress user database. Or it might be simpler to just let WorPress use the custom user database to begin with.
The purpose of the custom user database is that I eventually want to also integrate it with other projects of mine and third party projects like phpBB etc. to allow for a single account throughout all those web-pages/-apps.
I'm not really comfortable with MySQL so I don't really know what the best way to do this would be. That's all I need to know though, after that I'll be able to get back to working on this.