codice:
...
<head>

<script language="javascript">
function insert(){
for(var z=0;z<2;z++){
to.nt_testo.value += mod.lol.option[z].value;
}
}
</script>

</head>
<body>
....

<form name="mod">
<select name="lol"  onChange="insert();">
<option> Scegli decorazione </option>
<option value="[B]"> Grassetto </option>
<option value="[I]"> Corsivo </option>
</select>
</form>

....

<form action="..." name="to">
<textarea name="nt_testo"></textarea>
/form>
Come stampo [B] in nt_testo(textarea).