te falto el codigo, dices que ya lo tienes no? si es así publicalo, si no, esto tardara un poco mas de tiempo

Codigo del menu:

Código: [Seleccionar]

// Show the menu up top. Something like [home] [help] [profile] [logout]...
function template_menu()
{
global $context, $settings, $options, $scripturl, $txt;

echo '
<div id="main_menu">
<ul class="Custom" id="menu_nav"><li><a><span><span></a></li>';

foreach ($context['menu_buttons'] as $act => $button)
{
echo '
<li id="button_', $act, '">
<a class="', $button['active_button'] ? 'active ' : '', 'firstlevel" href="', $button['href'], '"', isset($button['target']) ? ' target="' . $button['target'] . '"' : '', '>
<span class="', isset($button['is_last']) ? 'last ' : '', 'firstlevel">', $button['title'], '</span>
</a>';
if (!empty($button['sub_buttons']))
{
echo '
<ul>';

foreach ($button['sub_buttons'] as $childbutton)
{
echo '
<li>
<a href="', $childbutton['href'], '"', isset($childbutton['target']) ? ' target="' . $childbutton['target'] . '"' : '', '>
<span', isset($childbutton['is_last']) ? ' class="last"' : '', '>', $childbutton['title'], !empty($childbutton['sub_buttons']) ? '...' : '', '</span>
</a>';
// 3rd level menus :)
if (!empty($childbutton['sub_buttons']))
{
echo '
<ul>';

foreach ($childbutton['sub_buttons'] as $grandchildbutton)
echo '
<li>
<a href="', $grandchildbutton['href'], '"', isset($grandchildbutton['target']) ? ' target="' . $grandchildbutton['target'] . '"' : '', '>
<span', isset($grandchildbutton['is_last']) ? ' class="last"' : '', '>', $grandchildbutton['title'], '</span>
</a>
</li>';

echo '
</ul>';
}

echo '
</li>';
}
echo '
</ul>';
}
echo '
</li>';
}

echo '
</ul>
</div>';
}

Y adjunta el index.css tuyo para meterle el css .