Tipo questo?

codice:
<div id="foo" style="background-color:#ff0000;"></div>

<form>
<select name="cities" id="cities" onchange = "update()"> <option value = "44">London</option> <option value = "40">Paris</option> </select>
</form>
clicca epr testare

<script>

function boh(){
if(document.getElementById('cities').selectedIndex>=0){
document.getElementById('foo').innerHTML=
document.getElementById('cities').options[document.getElementById('cities').selectedIndex].text;
}
else{}
}

</script>