Das Menü

body {
  margin: 20px;
  background-color: #0080c0;
}
#menu {
  float: right;
  width: 150px;
  height: 300px;
  margin-left: 20px;
  background-color: #ffcc00;
}
#inhalt {
  float: right;
  width: 78%;
  background-color: #ffffc6;
}
p.zurueck {
  clear: right;
}

...

<div id="menu">...</div>
<div id="inhalt">...</div>
<p class="zurueck">...</p>