function popup( url, title, windowWidth, windowHeight )
{
	var newWindow;
	var myleft = ( screen.width ) ? ( screen.width - windowWidth ) / 2 : 100;
	var mytop  = ( screen.height ) ? ( screen.height - windowHeight ) / 2 : 100;
	var properties = 'scrollBars=no,resizable=no,toolbar=no,menubar=no,location=no,directories=no,width=' + windowWidth + ',height=' + windowHeight + ',top=' + mytop + ',left=' + myleft + '';
	newWindow = window.open( url, title, properties );
}