plugin to auto register users from separate DB
 

i have a site - without a forum - where users register to download content for free or for fee. I currently have 150,000 users.

i added a vb forum. i'd like to provide users with an easy way to become a forum member by 'auto' creating their forum account if they wish. The auto creation would simply grab their email and pw from a separate DB.

I envision a link that lands on vb's reg page with email and pw pre-filled.Is there an easy way to do this, a plugin of similar capability perhaps?

My ultimate goal is to make it a breeze for existing (non-forum) users to engage in the forum.

thanks.