Current site and vbulletin
 

Right now we're running a membership based site, and we have a mysql database which holds the username data. We don't have a forum atm and we're hoping to use vbulletin as our new forum :). But we dont want our users to signup as new users for our new forum. We want to integrate it with the current users details. We're using md5 to encrypt our user passwords. So my questions are,

Can I use custom, username, email and password field from a difference database? or Is there any method to import our users data in to vbulletin? :confused:

You can use ImpEx (import script that comes with vBulletin) to create the user accounts. In most cases passwords will need to be reset.