A simple way of doing this would be to store the admin information in a database (or file if you don't have access to a database). Then on the index.php (or what ever page is loaded by default) check to see if the user has a cookie (a small bit of information that is can be stored on each connecting computer) with a correct [pseudo]random string.

If the strings match you can assume that the connecting user has either copied the data or is an admin. If the user appears to be valid you could send them to page1.php (where you would want to validate again) or if they don't then off to page2.php.

If you have any specific questions (or about the flow of a basic authentication system) don't hesitate to ask.

__________________
My Site