Ajax and custom function.

If you want instead of adding event to button in custom form to add ajax to some link (javascript function) here is how you can do it: 

function show(options)
         {
           $('update').innerHTML = '<div align=".'"center"'.">
  <img src="/.'"images/ajax-loader.gif" width="66" height="66"/>'."<p/>Please wait</div>'
           var ajaxRequest = new Ajax('index.php', {
                   method: 'get',
                   onComplete: function(response) {
                       $('update').innerHTML = response;
                   }
               });
               ajaxRequest.request(options);
}

Where options are variables which you sent through ajax, for example:

<a onclick="show('option=com_regdavzav&task=result&format=raw&pageNumber=2&naziv=ANGEL')" href="#">2</a>

It seems that mootools which are coming with Joomla! old, so documents about mootools which are in Joomla! you can find here.