function popup(url, width, height, top, left) {
	
	var height = (height || 70);
	var width = (width || 350);	
	
	height += 50;
	
	if (!top) {
		var fullHeight = screen.availHeight - 25;		
		top = Math.round((fullHeight / 2) - (height / 2));
	}
	
	if (!left) {
		var fullWidth = screen.availWidth - 10;		
		left = Math.round((fullWidth / 2) - (width / 2));
	}

	var wind = window.open(url, 'popup_window', 
		"width=" + width + ", height=" + height + ","
			+ "top=" + top + ", left=" + left + ", toolbar=no, scrollbars=auto, menubar=no, status=no, resizable=yes", true);
			
	wind.focus();
}