function abrirventana(url,width, height)
{
	if(document.all)
	{
		izq = (screen.availWidth) ? (screen.availWidth-width)/2 : 0;
		alt = (screen.availHeight) ? (screen.availHeight-height)/2 : 0;
	}else{
		izq = (screen.width) ? (screen.width-width)/2 : 0;
		alt = (screen.height) ? (screen.height-height)/2 : 0;
	}

	ventana = window.open(url, '', "toolbar=0,location=0,directories=0,status=0,menubar=0,scrollbars=1,resizable=1,left=" + izq + ",top=" + alt + ",width=" + width + ",height=" + height);
	ventana.focus();
}