Código PHP:
<script>
function funcion(){
if(document.formulario.box.checked == true){
document.formulario.nombre.disabled = false;
document.formulario.campo2.disabled = false;
}
else{
document.formulario.nombre.disabled = true;
document.formulario.campo2.disabled = true;
}
}
</script>
<form name="formulario">
<input type="checkbox" name="box" onclick="funcion()" />
<input type="text" name="nombre" disabled />
<input type="text" name="campo2" disabled />
</form>
