:nth-child() failing in ie7

:nth-child() failing in ie7

$(xml).find('model').each(function(){
      var $obj = $(this)
      _model = $obj.find('data:nth-child(3)').text();
      _fuelType = $obj.find('data:nth-child(5)').text();
      _city_mpg = $obj.find('data:nth-child(6)').text();
      _combined_mpg = $obj.find('data:nth-child(7)').text();
      _hwy_mpg = $obj.find('data:nth-child(8)').text();
      
      var values = _model + "," + _fuelType + "," + _city_mpg + "," + _combined_mpg + "," + _hwy_mpg;
                  var options = '<option value="' + values + '">' _model</option>';
                  
                  $("select#model").append(options).attr("disabled", false);
                  
               });


'data:nth-child()' seems to throw an error in ie. I can get 'data:first' and this works fine but nth-child breaks it.
Anyone ever come across this in your travels?