Modify menus HTML output

I’m trying to add the sub-wrapper div (nav-holder) into the menus HTML output. Any suggestions on how to do this? Do I have to use a nav walker for this or can I use a filter? Any good tuts out there on styling WordPress menus?

WordPress generates this code

<div id="header" class="main-menu">
	<ul id="menu-top" class="menu">
		<li></li>
	</ul>
</div>

I want this code generated. I want to add the .nav-holder wrapper

<div id="nav" class="home">
	<div class="nav-holder">
		<ul>
			<li></li>
		</ul>
	</div>
</div>

Thanks!