document.cancel()

[Reale_Augello]

... prova così:

<script>
function sel()
{
menuc=document.formc.menuc.value;
switch(menuc) {
 case 1:
 document.getElementById('livello').innerHTML='
aaaaaaaaaaaaaa';
 break;
 case 2:
 document.getElementById('livello').innerHTML='
bbbbbbbbbbbbbb';
 break;
 case 3:
 document.getElementById('livello').innerHTML='
cccccccccccccc';
 break;
 }
}

</script>
<div id="livello"></div>

Ciao !