#menu{
width:100%;
background-color:#000;
position:absolute;
top:0px;
left:0px;
border:solid;
border-color:#0F0;
border-right:none;
border-top:none;
border-left:none;
}
#menu ul li{
display:inline;
padding-left:30px;
}
#menu ul{
padding-top:3px;
padding-bottom:3px;
}
#menu ul li a{
font-size:11px;
color:#CCC;
text-decoration:none;
}
#menu ul li a:hover{
color:#FFF;
}
#logo{
background-color:#F00;
width:100%;
height:300px;
}
<!DOCTYPE html PUBLIC "-//W3C//DTD XHTML 1.0 Transitional//EN" "http://www.w3.org/TR/xhtml1/DTD/xhtml1-transitional.dtd">
<html xmlns="http://www.w3.org/1999/xhtml">
<head>
<meta http-equiv="Content-Type" content="text/html; charset=utf-8" />
<title>Untitled Document</title>
<link rel="stylesheet" type="text/css" href="estilos.css" />
</head>
<body>
<div id="menu">
<ul>
<li><a href="index.php">PRINCIPAL</a></li>
<li><a href="cfg.php">CFG</a></li>
<li><a href="ftp.php">FTP</a></li>
<li><a href="contacto">CONTACTO</a></li>
</ul>
</div>
<div id="logo">
</div>
<div id="contenido">
</div>
</body>
</html>