[juven14]

I was referring to the folder where you have vbulletin itself installed.

The prefix is just something added to the tables to help you seperate other scripts in the database. The default for the classifieds is class_

I share the same database just because it makes it easier for me to pull down information from both at the same place. This does make backups and restores a little more work as both your classifieds and forum can take up some space.

I think it might be easier for you to manage if you create a new database for vbulletin, and then once you have vbulletin installed then get the info you used when installing vbulletin and use it in the settings.php.