I've got a site with ~500 registered members, 300 of which are what you'd call "active". Site data is kept in a MySQL dbase.

I'd like to add a myBB forum to the site, but this question applies to any forum really.

What I very much want to avoid is requiring my users to register both on the site and on the forum because my userbase is not technically literate and this would confuse a lot of them.

However the forum software has its own registration, login, cookie, and password management system which naturally are different from the site's mechanics.

I envision the following possibilities:

• install myBB into the existing database and customize the login code to unify the two systems. This would probably mean changing the site's code to use the myBB system as that would likely be less painful to refactor and wouldn't hurt future myBB upgrade ability.
• install myBB into separate database and write a bridging script of some sort that auto-registers existing site users with the forum if they elect to participate. Also check new forum registrations against the site's username list to prevent newcomers from taking existing names.
• run them fully separate and force users to re-register (easiest for ME, but least desirable for them)

I would like a suggested course of action from those who have trod this path before...

Thank you.