Element.Update scriptaculos issue :S

[eluser]Peter74[/eluser]
Hi all! learning ci a couple of weeks.. almost ready for start my first proyect, before i want learn ajax, y read the documentation from the site, and learn with Derel Allard and iam try to Update one segment of the page but dont work..
look at this
please

Code:

myfunc.js
window.onload = function(){
    $('mainmenu').onclick = function(){
    //new Element.update('contenido','static content');    //this work
    new Element.update('contenido', base_url+'contenido/menu');  //dont work
    return false;
    }
}

i think i need to know, how to put a "variable" in the second parameter of the function element.update

Code:

contenido.php
<?php
class Contenido extends Controller{
function index(){
    echo "estoy en contenido :D";
}
function menu(){
   $select = $this->uri->segment(3);
   //this is ok, i load the content of the file... (menu choosen)
   $data['contenido'] = $this->load->view('segmentos/'.$select.'_inc.php', '', true);
   //echo $data['contenido'];                          i try with this, no work
   //echo $this->input->post($data['contenido']);      i try with this, no work
   //return $data['contenido'];                        i try ...
    }    
}
the view
<?php
    $this->load->view('header');
?>
    <div id="contenido" class="fila">
    &lt;?php echo $contenido; ?&gt;        
    </div>
&lt;?php
    $this->load->view('footer');
?&gt;

Any help or sugestion helpe a lot, very txs for reading and reply

[eluser]Peter74[/eluser]
i found some mistakes and now the problem is
new Element.update('contenido', base_url+'contenido/menu');

base_url is not defined

[eluser]chreestopher[/eluser]
I have had the same problem. I found this declared on the page and it fixed my problem. works great now.

Code:

//<![CDATA[
base_url = '<?=site_url();?>';
//]]>

Thanks for the tutorial