how to hide some content on webpage from unregistered user ?

I am using PHP Login Script from about.com

http://php.about.com/od/finishedphp1/ss/php_login_code.htm

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use a session variable. if set (login) show, if not, don't.

ardav is right...just when a user login...set a session variable for him....
And for every page include the script to check whether session variable is set or not otherwise they may try to enter in some other page without login...
or just make a page to check whether session id is set or not and include that page before every page....