gistfile1.js

function toggleInputs(){
  //replace the placeholder names below
  var inputs = $('theNameOfYourSecondaryBox').select('input,select,textarea');
  var checkbox = $('theIdOfYourCheckbox');
  //all the rest of this can stay the same
  if(checkbox.checked){
    inputs.invoke('disable');
  }else{
    inputs.invoke('enable');
  }
}
//be sure this matches the name of the box also
$('theIdOfYourCheckbox').observe('click',toggleInputs);