Code: 
body {
background-color: #006699;
background-image: url(images/seiten_verlauf_oben.gif); 
background-repeat: repeat-x;
background-position: top;
...
}

#main {
margin-top: 10px;
margin-left: 10px;
background-image: url(images/seiten_verlauf_unten.gif); 
background-repeat: repeat-x;
background-position: bottom;
}