you could create a php include file that will first check the username/pass against an encrypted database password then create a cookie.
Then by placing this include file on every page, the site can check to see if the right person is logged in - if not it kicks them back to the login page. Of course you would have to create a random string that's stored in the cookie and again in the database. That's how the system knows if you're logged in or not.
Check www.hotscripts.com there are plenty of tutorials and scripts for doing this if you can't be bothered writing it from scratch. 😉
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