how do I? importing user names and passwords from another web service to vbulletin

[bunder]

I have a web site in which people need to register and they choose their own user name and password in order to access the site and the content on the site.

I am looking to have forums on this site and would like it so that users have one log in which also gives them access to the forums.

All user data is kept in a mySQL database.

So the question is... How easy is it to then set up vbulletin and automatically import the user name and passwords, so that users automatically have a log in and password.

Of course, some of the data that a vbulletin forum asks for, the user has not already given me. But I am not too bothered about that, only importance is user name, password and e-mail address which I have along with date of birth as well.

Any advice from the pros here on how they would do it and also any advice from someone who has actually done it.

thanks!

Leslie