Security

Hi I have a MySql database running a PHP3 driven site. There is a directory off the main site called the Admin directory - where the PHP pages are located to add/remove/edit information stored in the database. Is there a simple include file written by anyone which I could use to authenticate the user of the Admin page - so that if someone stumbled accross the address, they couldn't access the pages. A simple Username and Password stored in the php script would surfice - but located in a database would be better. Thanks Tom Peck