Abilitare/Disabilitare campi form

[superesse]

<script language="javascript" type="text/javascript">
function fun_sblocca(){
if (document.form1.nodialogo.checked== false) {
document.form1.descrizione.disabled = false;
document.form1.dialogo.disabled = false;
document.form1.epilogo.disabled = false;
} else {
document.form1.descrizione.disabled = true;
document.form1.dialogo.disabled = true;
document.form1.epilogo.disabled = true;
}
return true;
}
</script>

<form method="post" action="dialogo_ok.asp" name="form1">
<textarea name="descrizione" cols="50" rows="5"></textarea>
<input type="checkbox" name="nodialogo" value=1 onclick="javascript:fun_sblocca();">
<textarea name="dialogo" cols="50" rows="5"></textarea>
<textarea name="epilogo" cols="50" rows="5"></textarea>
</form>

Ciao