New in vBulletin 5 is the Presentation configuration file. It is always located in the forum root or / directory of your vBulletin package. In a newly unzipped package, this would be the upload folder.
It is named config.php.bkp. Rename this file to config.php by removing the .bkp extension.
This file no longer needs to be edited to perform an installation. It is there for support purposes only.