Newb: Linking logins.

[smashtheqube]

Okay, I'm really sorry... I literally haven't run a vBulletin forum since about 2003.

My question is:
I have a site that I want to add a forum to, paralleling our existing userbase.

Solutions I've thought of:
1) Editing register.php to disable the email and password inputs (we have those) but leaving nickname (which they need to choose)
2) Manually creating user-data (as new-users "activate" the forum) using my own MySQL calls from our application.

I mean the only downsides to these are that #1 has to be updated if vBulletin's code changes and #2 has to be updated if their database requirements change. But, with either of these the user's email address and other info is not synced.

Am I doing this wrong?? What should I do...