codice:
  <script language="JavaScript" type="text/javascript">
<!--
 s = document.form2.d.value
 c = s.split("/")
 o = new Date(c[2], c[1]-1, c[0])
 w = o.getDay()

function test1(value) {
 if (value == '3') {
  document.getElementById('giorno').options[3].selected = true;  //abilitata
 } else {
  document.getElementById('giorno').options[3].selected = false;  //disabilitata
 }
 }
//--> 
 </script>

<input name="d" id="d" readonly value="" type="text" class="contact" onChange="test1(this.value)" />



<select name="giorno" onChange="test(this.value)">
<option value="">Inserire il giorno</option>
<option value="Martedì">Marted&igrave;</option>
<option value="Mercoledì" id="3">Mercoled&igrave;</option>
<option value="Giovedì">Gioved&igrave;</option>
<option value="Venerdì">Venerd&igrave;</option>			
<option value="Sabato">Sabato</option>
</select>
ma non va...