Hola, Sofía
Esto te puede valer:
Código HTML:
<head>
<script type="text/javascript">
function valida(formu)
{ var op = ""
for (var i=0; i<formu.info.length; i++)
{ if (formu.info[i].checked) op=formu.info[i].value }
if (op=="si")
{ for (i=0; i<formu.frec.length; i++) { formu.frec[i].disabled=false }
for (i=0; i<formu.forma.length; i++) { formu.forma[i].disabled=false }
}
}
</script>
</head>
<body>
<form>
Recibir información:
<input type="radio" name="info" value="no" onClick="valida(this.form)">No
<input type="radio" name="info" value="si" onClick="valida(this.form)">Sí
<br>Frecuencia
<input type="radio" name="frec" checked disabled="true">A
<input type="radio" name="frec" disabled="true">B
<br>Formato
<input type="radio" name="forma" checked disabled="true">A
<input type="radio" name="forma" disabled="true">B
</form>
</body>