Pop up window - JQuery Script

<script type="text/javascript" src="http://ajax.googleapis.com/ajax/libs/jquery/1.4.2/jquery.js"></script>
<script type="text/javascript">
$(document).ready(function() {

	if (once_per_session==0)
		loadpopunder()
	else
	{
	if (get_cookie('popunder')==''){
		loadpopunder()
		document.cookie="popunder=yes"
	}
	}



});
</script>

<script type="text/javascript">

//Pop-under window II- By JavaScript Kit
//Credit notice must stay intact for use
//Visit http://javascriptkit.com for this script

//Pop-under only once per browser session? (0=no, 1=yes)
//Specifying 0 will cause popunder to load every time page is loaded
var once_per_session=1

///No editing beyond here required/////

function get_cookie(Name) {
  var search = Name + "="
  var returnvalue = "";
  if (document.cookie.length > 0) {
    offset = document.cookie.indexOf(search)
    if (offset != -1) { // if cookie exists
      offset += search.length
      // set index of beginning of value
      end = document.cookie.indexOf(";", offset);
      // set index of end of cookie value
      if (end == -1)
         end = document.cookie.length;
      returnvalue=unescape(document.cookie.substring(offset, end))
      }
   }
  return returnvalue;
}

function loadornot(){
if (get_cookie('popunder')==''){
loadpopunder()
document.cookie="popunder=yes"
}
}
function loadpopunder(){
var id = '#popup';


		//Get the screen height and width
		var maskHeight = $(document).height();
		var maskWidth = $(window).width();

		//Set heigth and width to mask to fill up the whole screen
		$('#mask').css({'width':maskWidth,'height':maskHeight});

		//transition effect
		$('#mask').fadeIn(1000);
		$('#mask').fadeTo("slow",0.8);

		//Get the window height and width
		var winH = $(window).height();
		var winW = $(window).width();

		//Set the popup window to center
		$(id).css('top',  winH/2-$(id).height()/2);
		$(id).css('left', winW/2-$(id).width()/2);

		//transition effect
		$(id).fadeIn(2000);


	//if close button is clicked
	$('.window .close').click(function (e) {
		//Cancel the link behavior
		e.preventDefault();

		$('#mask').hide();
		$('.window').hide();
	});

	//if mask is clicked
	$('#mask').click(function () {
		$(this).hide();
		$('.window').hide();
	});
}

</script>