Styles, style.css:
<code lang="CSS">
body {
	margin: 32px 0 0 0;
}
#toolbar {
	display: block; 
	padding: 0 40px; 
	margin: 0; 
	background-color: #333; 
	border-bottom: 2px solid #AAA;
	height: 30px; 
	position: fixed; 
	width: 100%; 
	top: 0; 
	left: 0; 
	opacity: 0.95; 
	list-style:none; 
	z-index: 1;
}
#toolbar li {
	float: left; 
	margin:0; 
	padding:0;
}
#toolbar li a {
	display:block; 
	padding:8px 15px 7px 15px;
	text-decoration:none; 
	font: bold 12px Arial, Helvetica, sans-serif; 
	color: white;
}
#toolbar li:hover ul {
	display: block;
}
#toolbar li:hover a {
	border-top: 2px solid white;
	padding-top: 6px;
}
#toolbar ul {
	display: none; 
	float: none; 
	position: absolute;
	margin: -5px 0 0 15px; 
	padding: 0; 
	list-style: none; 
	z-index: 2;
	border-bottom: 2px solid black;
	background-color: white;
	opacity: 0.9;
}
#toolbar ul li {
	margin: 0;
	padding: 0;
	display: block; 
	float: none;
}
#toolbar ul li a {
	width: 150px;
	margin: 0;
	padding: 8px 15px 8px 15px;
	display: block;
	float: none;
	font: bold 12px Arial, Helvetica, sans-serif;
	color: black;
}
#toolbar ul li a:hover {
	background-color: #DDD;
}

/* for IE 6 and below, because they do not support position: fixed; */
<!--[if lte IE 6]>
@import "iehack.css"
<![endif]-->
</code>

IE 6 and below hack, iehack.css:
<code lang="CSS">
BODY { margin: 0; }
#toolbar { position: absolute; }
</code>

The HTML:
<code lang="HTML">
<ul id="toolbar">
  <li>
    <a href="javascript:void(0)">Item one</a>
      <ul>
        <li><a href="#">Something</a></li>
        <li><a href="#">Something</a></li>
        <li><a href="#">Something</a></li>
        <li><a href="#">Something</a></li>
      </ul>
  </li>
  <li>
    <a href="javascript:void(0)">Item two</a>
      <ul>
        <li><a href="#">Something</a></li>
        <li><a href="#">Something</a></li>
      </ul>
  </li>
  <li>
    <a href="#">Item Three</a>
  </li>
</ul>
</code>