beh, in verità non vedo la pesantezza di 64Kb di script, comunque, puoi sempre (sul sito di Mootools) indicare cosa ti serve e per qeusto ti basta il core e gli element.
Detto ciò
crea una struttura tipo:
	Codice PHP:
	
<div id="tot">
    <div id="header">
        <ul  class="tabs-header">
            <a href="#" onclick="change('uno')">
                [*]
                    Uno
                
            </a>
            <a href="#" onclick="change('due')">
                [*]
                    Due
                
            </a>
        [/list]
    </div>
    <div id="content">
        <div class="tabs" id="uno">
            <h1>Contenuto 1</h1>
            askjbdsjkbjkbgfkjbagkjakjasfgbbz
            askjbdsjkbjkbgfkjbagkjakjasfgbbz
            askjbdsjkbjkbgfkjbagkjakjasfgbbz
            askjbdsjkbjkbgfkjbagkjakjasfgbbz
        </div>
        <div class="tabs" id="due">
            <h1>Contenuto 2</h1>
            askjbdsjkbjkbgfkjbagkjakjasfgbbz
            askjbdsjkbjkbgfkjbagkjakjasfgbbz
            askjbdsjkbjkbgfkjbagkjakjasfgbbz
            askjbdsjkbjkbgfkjbagkjakjasfgbbz
        </div>
    </div>
</div> 
 
Con CSS 
	Codice PHP:
	
<style type="text/css">
            #tot{
                width: 800px;
                margin: 50px auto 0px auto;
            }
            
            #header{
                width: 100%;
                height: 20px;
                float: left;
            }
            
            #content{
                width: 100%;
                height: auto;
                float: left;
                border: 1px solid silver;
                background-color: #FFE87C;
            }
            
            .tabs-header{
                list-style: none;
                margin: 0px;
                padding: 0px;
            }
            
            .tabs-header li{
                width: 100px;
                height: 20px;
                float:left;
                text-align: center;
                border-top: 1px solid silver;
                border-left: 1px solid silver;
                border-right: 1px solid silver;
                
            }
            
            .tabs-header li.active{
                background-color: #FFE87C;
            }
            
            .tabs{
                width: 100%;
                float: left;
                display: none;
            }
</style> 
 
e Javascript
	Codice PHP:
	
var active = 'uno';
window.onload = function(){
    change(active);
}
function change(id)
{
    var el = document.getElementById('content');
    var divs = el.getElementsByTagName('div');
    var index = 0;
    for(i = 0; i < divs.length; i++)
    {
        if(divs[i].id == id)
        {
            divs[i].style.display = 'block';
            index = i;
        }
        else
        {
            divs[i].style.display = 'none';
        }
    }
    
    el = document.getElementById('header');
    var lis = el.getElementsByTagName('li');
    for(i = 0; i < lis.length; i++)
    {
        if(i == index)
        {
            lis[i].className = 'active';
        }
        else
        {
            lis[i].className = '';
        }
    }
} 
 
Dovrebbe funzionare