Może Ci się przyda - z jakiegoś starego kodu wyciągnąłem;
if (!isset($_SESSION[okno
])) {
<script type="text/javascript">
function show () {document.getElementById(\'popup\').style.display="block";}
function hide () {document.getElementById(\'popup\').style.display="none";}
</script>
<div id="popup" style="display:block; position: absolute; top: 50px; left: 0; width: 100%; text-align: center; z-index: 1111;">
<div style="position:relative; z-index:11155; top:0px; left:0; height:600px; width: 466px; margin:0 auto; text-align:center; background:white; padding:10px;">
<a href="java script:hide();" style="position:absolute; top:10px; left:10px; z-index:11160; display:block; width:447px; height:400px;" >
Jakaś treść <img src="jakas_fotka.jpg" alt="ida swieta" style="z-index:11162;"/>
</a>
<div style="position:absolute; right:0px; top:0px; z-index:11163;">
<a href="java script:hide();" ><img src="closebox.png" alt="zamknij" style="z-index:11161;"/></a>
</div>
</div>
</div>';
}
$_SESSION[okno] = true;