Registration done on both site and vbulletin at the same time?
 

let says for example i have a site (not vb forum) where users sign up and register an account to use the services of the site.
also, i have vbulletin integrated into this site where users would have to register an account in order to use the forum.
how difficult would it be to have my site's registration page register users for vbulletin as well?
sort of like killing two birds with one stone.

any help to finding a solution on how to achieve this will be greatly appreciated.

thank you