function openPopup(_object) {
	var _top;
	var _left;
	// centramos la ventana
	_top = (screen.availHeight/2) - (_object._height/2);
	_left = (screen.availWidth/2) - (_object._width/2);
	if(typeof(_object._scrollbar) == "undefined") {
		_object._scrollbar = "0";
	}
	// creamos las ventanas
	eval("page" + _object._name + " = window.open(_object._url, '" + _object._name + "', 'toolbar=0,scrollbars=" + _object._scrollbar + ",location=0,statusbar=0,menubar=0,resizable=0,width=" + _object._width + ",height=" + _object._height + ",left=" + _left + ",top=" + _top + "');");
	_top = null;
	_left = null;
}