easiest way to do this is using phpmyadmin. There is no magic command for this. There is a linux command to backup a database and restore it. However it can get complicated and if you do the wrong thing you can wipe out the database. This article explains the basics of this command
http://gentoo-wiki.com/HOWTO_Backup_MySQL
Just backup the photopost database and restore that backup to the vbulletin database. You then edit your config settings in photopost to point to the
vb database and see if everything is working