Hola
PedroRodas
Un ejemplo rápido:
Código PHP:
<!DOCTYPE html PUBLIC "-//W3C//DTD XHTML 1.0 Transitional//EN" <html>
<head>
<script type="text/javascript">
function habilitar(valor) {
frm = document.forms[0];
for (i=0; ele = frm.elements[i]; i++)
if (ele.type == 'checkbox')
ele.disabled = (ele.className != valor);
}
</script>
</head>
<body>
<form>
<select onchange = "habilitar(this.value)">
<option value="coches">Coches</option>
<option value="aviones">Aviones</option>
</select>
<input type="checkbox" class="coches" disabled = "disabled" />
<input type="checkbox" class="aviones" disabled = "disabled" />
<input type="checkbox" class="coches" disabled = "disabled" />
</form>
</body>
</html>
Saludos,