[poorking]

<style type = "text/css">
ul{
	width: 100px;
	border: 1px solid red;
}
.with_sub{
	position:relative;
}
.with_sub ul{
	display: none;
	position: absolute;
	top:0px;
	left: 100%;
}
.with_sub:hover > ul{
	display: block;
}
</style>

<ul>
	<li>item 1</li>
	<li class = "with_sub"><div>item 2 (sub)</div>
		<ul>
			<li>sub 1</li>
			<li class = "with_sub"><div>sub 2(sub sub)</div>
				<ul>
					<li>sub sub 1</li>
					<li>sub sub 2</li>
					<li>sub sub 3</li>
					<li>sub sub 4</li>
				</ul>
			</li>
			<li>sub 3</li>
		</ul>
	</li>
	<li>item 3</li>
</ul>

так?