window.addEvent(
  'domready',
  function()
  {
    var searchInput = $('suchbegriff');
    completer = new Autocompleter.Ajax.Json(
      searchInput,
      '/autocomplete.php',
      {
        'onSelect': function()
        {
          $('suchform').submit();
        },
        'useSelection': false
      }
    );
  }
);