it's little bit tricky, because u'll need do changes in two files and create new template....
if u still want it, then in /includes/functions.php find:function get_category_dropdown($cat_id = 0, $jump = 0, $admin = 0, $i = 0) {
replace with:function get_category_dropdown($cat_id = 0, $jump = 0, $admin = 0, $i = 0, $name_form = "jumpbox") {
then find:$category = "\n<select name=\"".URL_CAT_ID."\" onchange=\"if (this.options[this.selectedIndex].value != 0){ forms['jumpbox'].submit() }\" class=\"categoryselect\">\n";
replace with:$category = "\n<select name=\"".URL_CAT_ID."\" onchange=\"if (this.options[this.selectedIndex].value != 0){ forms['".$name_form."'].submit() }\" class=\"categoryselect\">\n";
then, open /includes/page_header.php find:$site_template->un_register_vars("category_dropdown_selfjump");
add right after:$category_dropdown_selfjump = get_category_dropdown($cat_id, 1, 0, 0, "jumpbox2");
$site_template->register_vars("category_dropdown_selfjump", $category_dropdown_selfjump);
$category_dropdown_form = $site_template->parse_template("category_dropdown_form2");
$site_template->register_vars(array("category_dropdown_form2" => $category_dropdown_form));
$site_template->un_register_vars("category_dropdown_selfjump");
then, create new template with name category_dropdown_form2.html
with this code:<table border="0" cellspacing="0" cellpadding="0">
<form method="post" name="jumpbox2" action="{url_categories}">
<tr>
<td>{category_dropdown_selfjump}</td>
</tr>
</form>
</table>
now use {category_dropdown_form2} tag to add second cat jump menu
good luck.