Código HTML:
<!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>Documento sin título</title>
<style type="text/css">
#top {
top:0px;
width:100%;
position:fixed;
background-color:#666;
}
body {
margin-left: 0px;
margin-top: 0px;
margin-right: 0px;
margin-bottom: 0px;
}
</style>
</head>
<body>
<div id="top">Colocar aquí el contenido para id "top"</div>
</body>
</html>