function popup( URL, w, h, scrollbars ) {
 var l = screen.width/2 - w/2;
 var t = screen.height/2 - h/2;
 var windowprops = "width="+ w +",height="+ h +",scrollbars="+scrollbars+",top="+ t +",left="+ l;
 newwindow = window.open( URL, '', windowprops);
 if (window.focus) { newwindow.focus() }
}