function pop_up(url,width,height)
	{
	if(window.screen)
	{
		var left=(screen.width-width)/2;
		var top=(screen.height-height)/2;
	}
	else
	{
		left=200;
		top=170;
	}
	params='height='+height+',width='+width+',status=no,toolbar=no,menubar=no,scrollbars=no,top='+top+',left='+left;
	var newwin = window.open(url,'address', params);
	newwin.window.focus();
	}