function checkAll(checkWhat) {
  // Find all the checkboxes...
  var inputs = document.getElementsByTagName("input");

  // Loop through all form elements (input tags)
  for(index = 0; index < inputs.length; index++)
  {
    // ...if it's the type of checkbox we're looking for, toggle its checked status
    if(inputs[index].id == checkWhat)
      if(inputs[index].checked == 0)
      {
        inputs[index].checked = 1;
      }
      else if(inputs[index].checked == 1)
      {
        inputs[index].checked = 0;
      }
  }
}