some questions about vb integration

[yayvb]

I purchased a script that is sort of like myspace. It's doing very good in it's first 30 days attracted about 1400 members. Besides needing some bugs fixed, and some features added, the forum that's included is garbage.

Since I own 2 copies of vbulletin, and neither is doing any good right now, I would love to replace the internal forum with vbulletin. I can disable menus and modify templates to get vbulletin looking great in the header and footer, etc.

What I'm not sure about is:
What's the best way to integrate the databases without hurting either script?

Would the best way be to make it so that when a member registers on my script, it also creates a valid registration on vbulletin?

I would like to have a single login obviously so when they go to the forum link, they're already logged in. Would I share cookies to do this so that vbulletin says ok that person has our cookie? Or would I just have the script also log them into vbulletin which may in the future present problems if they change their login info for my script right? Unless I make further modifications to also update vbulletin, or maybe even just store the original registration email and password in the database in a vb section and disable the ability to change vbulletin email/password.

There must have been many different scripts being integrated with and without vbulletin involved. Any direction would be appreciated.