Redirecting

Hey all, Just curious as to what the best way is to move someone off your site, apart from bringing up a picture of male pornography... Seriously, I've tried using header("Location: http://www.php.net/"); but it returns an error saying that the headers are already set. The situation I'm in is as follows: Need to send a user to http://www.examplesite.com/ from a PHP script in http://forums.examplesite.com/ Thanks for the help