var X=960;
var Y=700;
//var L = (screen.availWidth/2) - (X/2);
//var T = (screen.availHeight/2) - (Y/2);


   var L = Math.floor((screen.width-X)/2);
   var T = Math.floor((screen.height-Y)/2);

function PrintPreview()
{
    var L = (screen.availWidth/2) - (960/2);
    var T = (screen.availHeight/2) - (700/2);
    window.open('ppreview.php','','width=960,height=700,toolbar=no,location=no,status=no,menubar=no,scrollbars=yes,resizable=no,left=' + L + ',top=' + T);
}