mysql_create_db function will not work on cPanel hosting. If you need to create database from your PHP script on cPanel hosted server then you'll need to use cPanel interface. Database creation code would look like (calling cPanel's adddb function): http://USER:PASS@HOST:2082/frontend/SKIN/sql/adddb.html?db=DB
You can download ready-made sample php script from http://www.zubrag.com/scripts/cpanel-database-creator.php