problem with drop down menu and child pages…

Hello!
i got Japanese Style theme installed and looks like that theme doesn’t support drop down menu (child pages). any idea what to change to get drop down menu working???
my *nav* code looks like:

<div id="nav">
		<ul>
			<li <?php if(!is_page()) echo 'class="current_page_item"'; ?>><a href="<?php echo get_option('home'); ?>/">Home</a></li>
			<?php wp_list_pages('title_li=&depth=0'); ?>
		</ul>

	      </div>

and my CSS for nav is:

/* Navigation
-------------------------------------------------------------------*/
#nav {
	width: 800px;
	height: 45px;
	margin-left: 30px;
	position: relative;
        top: 225px;
}
#nav ul {
	margin-left: 10px;
	position: absolute;
	bottom: -1px;
	overflow: hidden;
	height: 45px;
}
#nav ul li {
	float: left;
	margin-right: 3px;
	padding-left: 3px;
        font-weight: bold;
}
#nav ul li.current_page_item {
        width: 122px;
        height: 45px;
}
#nav ul li a {
        width: 122px;
        height: 45px;
        background: url(images/nav_bg.jpg) no-repeat;
	display: block;
	text-decoration: none;
	color: #333;
	line-height: 45px;
	text-align: center;
}
#nav ul li a:hover { color: #555; }
#nav ul li.current_page_item a { background: url(images/nav_bg.jpg) no-repeat; color: #ff0000; }