Simple If Statement

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I am trying to make it so that if a user is unregistered then they get forwarded to the forum section of my VB4 page. If they are registered then they get sent to the CMS page.

I already located the code in the index page. Just don't know the variables for the VB back end to write the script.

PHP Code:

 * Use the CMS as the default script:
 */

require('content.php');


/**
 * Use the forum as the default script:
 */

// require('forum.php'); 


Any help would be appreciated.