Se ti può interessare puoi ottenere un effetto quasi simile col solo css, senza javascript…

codice:
<!doctype html>
<html>
<head>
<meta http-equiv="Content-Type" content="text/html; charset=UTF-8" />
<title>Pagina vuota</title>
<style>
div#menu {
	width: 170px;
	margin-left: 30px;
	background: #00005A;
	border: 1px solid #00005A;
	font: 11px Arial, Helvetica, sans-serif;
}

div#menu h3 {
	font-size: 100%;
	margin: 0;
	padding: 4px 10px;
	border-top: 1px solid #FFF;
	color: #000;
	background-color: #7BA5E7;
}


div#menu h3:hover {
	background-color: #FFFF00;
}
div#menu ul, div#menu ul li {
	margin: 0;
	padding: 0;
	list-style-type: none;
}

div#menu ul li {
	margin: 0 0 1px 0;
}

div#menu a {
	display: block;
	padding-left: 15px;
	height: 18px;
	line-height: 18px;
	border-top: 1px solid #FFF;
	background-color: #BDBDBD;
	color: #000;
	text-decoration: none;
	font-weight: bold;
}

div#menu ul li ul li {
	display: none;
}

div#menu ul li:hover ul li {
	display: block;
}

div#menu a:hover {
	color: #00005A;
	background-color: #0099FF;
}

div#menu ul li ul li a {
	color: #333;
	background-color: #AECDFF;
	font-weight: normal;
}
</style>
</head>

<body>
<div id="menu">
<ul>[*]Home Page[*]<h3>Linguaggi</h3>
        <ul>[*]CSS[*]Javascript[*]DOM
[*]PHP[/list]
    [*]<h3>Software</h3>
        <ul>[*]Photoshop[*]Flash
[*]Fireworks[*]Dreamweaver[/list]
    [*]<h3>Webdesign</h3>
        <ul>[*]Webdesign
[*]Accessibilità[*]Usabilità[/list]
    [/list]
</div>
</body>
</html>