get_terms() with javascript?

Hey guys,

I have the following situation:
For one of my Websites I need a extended Searchform (taxonomy picking). This is my code, so far:

<select id="hersteller" name="hersteller" onchange="showTextBox(this.value)+showcategory(this.value)">
<option value="Hersteller">Hersteller</option>
<?php $terms = get_terms('category');
foreach ($terms as $term) { printf( '<option id="hersteller" class="level-0" value="%s">%s</option>', $term->slug, $term->name ); </select>

<div id="modell" style="display:none">
<select name="Modell">
<option value="Modell">Modell</option>
<?php $terms = get_terms('marke-<strong>HERE GOES THE SELECTED CATEGORY</strong>'); 

foreach ($terms as $term) { printf( '<option class="level-0" value="%s">%s</option>', $term->slug, $term->name ); } ?>
</select>
</div>

Inside get_terms(”) some javascript needs to pick the selected category name. For this I tried a function:

get_terms('marke-'.'<script type="text/javascript">
function showcategory(made){document.write(hersteller.options[hersteller.selectedIndex].value;
}</script>'.'');

It did not work at all, I tried so much more, but nothing helped. Does anyone have an idea? I am very happy about any suggestion!!

Cheers Felix