#top-container { 
  width: 780px;   /* base top-container width (600) plus margin (20) plus ad width (160) */
}

#top-frame { 
  float: left;
}

#advertisement { 
  width: 160px;
  float: right;
  margin-right: -20px;
}

#bottom-margin { 
  float: left;
  clear: both;
  height: 50px;
}