How to add a drop down menu to this wp theme?

Hi everyone,

I downloaded the watermelon theme free available at: http://wpthemeland.com/theme/Watermelon/

I just wanted to know how to i make a drop-down menu with that theme?

This is the menu code:

<div class="nav">

	<div class="l">	</div>

	<div class="r">	</div>

	<ul class="artmenu">

		<?php art_menu_items('title_li=&sort_column=menu_order&depth=2'); ?>

	</ul>

</div>

Code (markup):

I have tried many ways to implement one.. Like plugins, adding another drop down menu and css etc, but all fail in the process

Can someone help??

Thanks,
Best Regards