function rand( min, max ) {
  var argc = arguments.length;
  if (argc === 0) {
      min = 0;
      max = 2147483647;
  } else if (argc === 1) {
      throw new Error('Warning: rand() expects exactly 2 parameters, 1 given');
  }
  return Math.floor(Math.random() * (max - min + 1)) + min;
}

$$('#dc-right .auto').setStyle('display', 'none');
$$('#dc-right .auto')[rand(0, $$('#dc-right .auto').length-1)].setStyle('display', 'block');