<input type="text" name="_id1:monthSpinner" value="0"/>

<script language="JavaScript">
   document['_id1']['_id1:monthSpinner'].spin = function (increment) {
      var v = parseInt(this.value) + increment;
      if (isNaN(v)) return;
      if ('min' in this && v < this.min) return;
      if ('max' in this && v > this.max) return;
         this.value = v;
   };
   document['_id1']['_id1:monthSpinner'].min = 1;
   document['_id1']['_id1:monthSpinner'].max = 12;
</script>

<input type="button" value="<"
      onclick="document['_id1']['_id1:monthSpinner'].spin(-1);"/>

<input type="button" value=">"
      onclick="document['_id1']['_id1:monthSpinner'].spin(1);"/>