function toggleImg(img) {
  src = img.src;
  if(src.indexOf('_off') != -1)
    img.src = src.replace('_off', '_on');
  else if(src.indexOf('_on') != -1)
    img.src = src.replace('_on', '_off');
}

function preloadImg(img) {
  src = img.src;
  document.onImg = new Image();
  document.onImg.src = src.replace('_off', '_on');
}

function validateEntry(form) {
  msg = "Please enter the following information:\n";
  valid = true;
  if ( form.first_name.value == "" ) {
    msg += "  First Name\n";
    valid = false;
  }
  if ( form.last_name.value == "" ) {
    msg += "  Last Name\n";
    valid = false;
  }
  if ( form.email.value == "" ) {
    msg += "  Email Address\n";
    valid = false;
  }
  if ( !valid )
    alert( msg );

  return valid;
}