function centerpopup(URL,Name,Scroll){

if (document.all) { 
   w = screen.availWidth;
   h = screen.availHeight;
}
else if (document.layers) {
   w = screen.availWidth;
   h = screen.availHeight;
}

var popW = 530, popH = 400;
var leftPos = (w-popW)/2, topPos = (h-popH)/2;

window.open(URL,Name,'scrollbars='+ Scroll +',width=' + popW + ',height='+popH+',top='+topPos+',left='+leftPos);

}