The only reliable method of backing up and restoring a database is with shell access via telnet or ssh (you might want to ask your host if they are willing ot restore for you if you don't have shell access). This is because backing up with a PHP script like that in the Admin CP or phpMyAdmin can result in PHP timeouts errors and an incomplete backup file. Please see the instructions here:
Backup:
http://www.vbulletin.com/docs/html/m...nce_ssh_backup
Restore:
http://www.vbulletin.com/docs/html/m...ce_ssh_restore
P.S. If you don't have shell access, some people have also reported success with these scripts:
MySQLDumper:
http://www.mysqldumper.de/en/index.php
MySQLHotxcopy:
http://www.vbulletin.com/forum/showt...t=mysqlhotcopy
Bigdump:
http://www.ozerov.de/bigdump.php