Edit skin1/help/contactus.tpl, lines 150-154 (for my version).
Look for:
Code:
<select name=department>
<option value="All" selected>{$lng.lbl_all}</option>
<option value="Partners">{$lng.lbl_partners}</option>
<option value="Marketing / publicity">{$lng.lbl_marketing_publicity}</option>
<option value="Webdesign">{$lng.lbl_web_design}</option>
<option value="Sales">{$lng.lbl_sales}</option>
</select>
You will have to login to the admin area and edit the variables you see above (lng.lbl_all, partners, etc). Or create new variables in the LNG section, OR just hard code the values in the TPL.
HTH.