I want to make a dynamic drop-down menu for the header that includes the TOP LEVEL categories, and listed below them, the FIRST SUB LEVEL categories - but no further. The idea is a menu similar to major e-commerce sites. A live example off the top of my head would be newegg.com

It needs to report the categories in the following way:

<ul>
<li>Top Cat 1</li>
<ul>
<li>Sub Cat A</li>
<li>Sub Cat B</li>
</ul>
<li>Top Cat 2</li>
<ul>
<li>Sub Cat C</li>
<li>Sub Cat D</li>
</ul>
<li>Top Cat 3</li>
(no sub categories)
</ul>

Currently it reports more something like this:

<ul>
<li>Top Cat 1</li>
<li>Top Cat 2</li>
<li>Top Cat 3</li>
</ul>

I know very little PHP and have been slowly moving along customizing the code... but this is a little over my head for doing it by myself I think.

I believe the code I need to change is in includes/modules/[MY TEMPLATE]/categories_tabs.php

Can anyone help me do this? I realize the basics of what needs to be done but don't know how to format the code, or all the 'commands' I need to use. Playing with it I was only able to get it to report sub categories and top level together.

THANKS IN ADVANCE!