function center_popup(url, name, width, height )
{
	window.focus() ; // so not to leave focus on link
	try {

		if(!url)		var url		= 'about:blank' ;
		if(!width)	var width	= 516 ;
		if(!height)	var height	= 420 ;
		if(!name)	var name	= '' ;
		
		var left		= (screen.width - width)/2 ;
		var top		= (screen.height - height - 100)/2 ;
		var tools	= 'width=' + width + ',height=' + height + ',left=' + left + ',top=' + top + ',resizable=yes,scrollbars=yes,toolbar=no,location=no' ;
		var popup	= window.open(url, name, tools) ;
		popup.focus() ;
		//return popup ;

	} catch(e){
		alert('To use this feature, please instruct your web browser to allow popups from this website.') ;
	}
}