PHP in header

[fulviods]

I need to urgently add this code on each page of my forum (4.2.0).
This code call images and css. This code shows to visitors coming from a specific website a popup (refered populp).
Where I can add it ??? I'm totally lost:

PHP Code:

<?php
if (!empty($_SERVER['HTTP_REFERER'])){
    $REFERED=$_SERVER['HTTP_REFERER'];
    
    $REFERED = parse_url($REFERED, PHP_URL_HOST);
}
else
{
  $REFERED='';
}
if ($REFERED=="www.website.com" OR $REFERED=="website.com" ):
?>
<script type="text/javascript" src="http://ajax.googleapis.com/ajax/libs/jquery/1.9.0/jquery.min.js"></script>
<script>
    $(document).ready(function(){ 
            setTimeout(function(){ 
                $('.overlay-bg').show("slow");
            }, 1000); 
            setTimeout(function(){ 
                $('.overlay-bg').hide("slow"); 
            }, 10000);     
            $('.close-btn').click(function(){
                $('.overlay-bg').hide("slow"); 
            });    
    });
</script>
<link href="overlaypopup.css" rel="stylesheet" type="text/css">
<div class="overlay-bg">
    <div class="overlay-content" id="popup">
        <div id="chiudi"><a href="#" class="close-btn"><img src="images/chiudi.png" /></a></div>
        <h1>WELCOME</h1>
        <ul>
            <li><img src="images/website_logo.jpg" /></li>
            <li><img src="images/mysite_logo.jpg" /></li>
        </ul>
        <div class="clear"></div>
        <p>
            text
        <a href="#" class="close-btn">See website</a>
        </p>
    </div>
</div>
<?php endif;?>

If anyone can help me it would be amazing! Thanks

--------------- Added [DATE]1379498782[/DATE] at [TIME]1379498782[/TIME] ---------------

i'm the only one that need some php code in the header of the forum?

[fulviods]

Finally found the solution https://vborg.vbsupport.ru/showthread.php?t=242454

[smirkley]

I like that code snippet you have posted above.

Is that like a welcome box that shows the referrer?