function changeadvertisement()
{
  var oIframe = document.getElementById('advertisement');
  var oDoc = (oIframe.contentWindow || oIframe.contentDocument);
  if (oDoc.document) oDoc = oDoc.document;
  oDoc.body.style.backgroundColor = "#aaa";
  oDoc.body.style.color = "#fff";
  oDoc.body.style.width = '200px';
  oDoc.body.style.height = '80px';
  return true;
}