function openPopup(url,popupName,popupW,popupH) {

	if (url == null) { url = "index.html"; }
	if (popupName == null) { popupName = "Untitled"; }
	if (popupW == null || popupH == null) { popupW = 600; popupH = 480; }

	var toolbar = 'no';
	var location = 'no';
	var directories = 'no';
	var status = 'no';
	var menubar = 'no';
	var scrollbars = 'no';
	var resizable = 'no';

	var screenW = screen.width;
	var screenH = screen.height;

	var popupX = Math.round((screenW-popupW)/2);
	var popupY = Math.round((screenH-popupH)/2 - 30);

	var features =	"toolbar=" + toolbar + ",location=" + location + 
					",directories=" + directories + ",status=" + status + 
					",menubar=" + menubar + ",scrollbars=" + scrollbars + 
					",resizable=" + resizable + 
					",width=" + popupW + ",height=" + popupH + 
					",left=" + popupX + ",top=" + popupY;

	var newPopup = window.open(url,popupName,features); newPopup.focus();

}