hola
luisicozgz
Prueba este ejemplo:
Código PHP:
<html>
<head>
<script type="text/javascript">
function habilita(obj) {
for (i=0; i<3; i++)
obj.form.rad[i].disabled = obj.selectedIndex==1;
}
</script>
</head>
<body>
<form>
<select onchange = "habilita(this)">
<option>Si</option>
<option>No</option>
</select>
<input type="radio" name="rad" />
<input type="radio" name="rad" />
<input type="radio" name="rad" />
</form>
</body>
</html>
Saludos,