Mine

<span class="autocomplete">
  <label for="owner">Add an owner:</label>   <input autocomplete="off" id="owner" name="owner" size="30" type="text" value="" /><input type="submit" name="submit" value="Add an owner" onclick="addItem($('owner').value);$('owner').value=''; return false;"/>


  <div class="auto_complete" id="owner_auto_complete"></div>
  <script type="text/javascript">new Ajax.Autocompleter('owner', 'owner_auto_complete', 
  '/task/auto_complete_for_owner/', {})</script>
</span>