Drop-down category navigation

Hello Guys, i need help to create a drop-down menu navigation for my sub-categories.

here’s the part from header.php i think i need to code, but i don’t know how to make it right.

"<div id="menu_container">

    <!--
        <ul class="pages_menu">

<li><a href="#">Home</a></li>
<li><a href="#">About</a></li>
<li><a href="#">Blog</a></li>
<li><a href="#">Contact</a></li>
        -->
        <?php wp_nav_menu('menu=header_menu&container=false&menu_class=pages_menu'); ?>

        <!--
        <ul class="cat_menu">

<li><a href="#">WebDesign</a></li>
<li><a href="#">Graphics</a></li>
<li><a href="#">Print</a></li>
<li><a href="#">Posters</a></li>
        -->
        <?php wp_nav_menu('menu=category_menu&container=false&menu_class=cat_menu'); ?>                

        <div class="clear"></div>

    </div><!--//menu_container-->"

from the “wp_nav_menu(‘menu=category_menu&container=false&menu_class=cat_menu’); ?> ” i’m sure i can do some coding with it and make it find my sub-category and make a dropdown menu.

thanks for help!

if you need more clue, please visit the site, you will know better why i need a drop down menu! https://hxxa.info