<form name="formulario">
<input type="checkbox" name="micheck" onClick="JavaScript:if(!this.checked){ for(i=0; i < document.formulario.miradio.length; i++){ document.formulario.miradio[i].disabled = true; }} else { for (i=0; i < document.formulario.miradio.length; i++) { document.formulario.miradio[i].disabled = false; }}" checked> <b>Frutas</b><br>
<input type="radio" name="miradio" value="manzanas"> Manzanas
<input type="radio" name="miradio" value="peras"> Peras
</form>