<a href="javascript://" onclick="openLayerB('USearch',0,'/usearch.xml','Расширенный поиск по
сайту',370,150,'1','','',0,'justify'); return false;">Поиск по
сайту</a>

function searchSelect(f) {
n = f.modul.selectedIndex;
modul = f.modul.options[n].value;
document.getElementById('search').action = 'http://ваш.адрес.сайта/'+modul+'/';
if (modul == 'news')
{
document.getElementById('a').value = '14';
}
else
if (modul == 'load' || modul == 'publ' || modul == 'dir' || modul == 'board')
{
document.getElementById('a').value = '2';
}
else
if (modul == 'blog')
{
document.getElementById('a').value = '13';
}
else
if (modul == 'faq')
{
document.getElementById('a').value = '3';
}
}

<?xml version="1.0" encoding="UTF-8"?>
<ajax>
<cmd p="jsa" t="USearch">
/usearch.js
</cmd>
<cmd t="layerContentUSearch" p="innerHTML"><![CDATA[
<div class="searchForm">
<form name="search" id="search" onSubmit="this.sfSbm.disabled=true" method="post" style="margin: 0px;">
<div class="schQuery" align="center">
<input name="query" maxlength="30" size="20" class="queryField" type="text">
<select name="modul" onChange="searchSelect(this.form);">
<option value="none">Где искать?</option>
<option value="news">Новости</option>
<option value="load">Файлы</option>
<option value="publ">Статьи</option>
<option value="dir">Сайты</option>
<option value="blog">Блог</option>
<option value="faq">ЧаВо</option>
<option value="board">Доска объявлений</option>
</select>
</div>
<div class="schBtn" align="center">
<input class="searchSbmFl" onClick="this.sfSbm.disabled=true" name="sfSbm" value="« Найти »" type="submit">
</div>
<input name="a" id="a" type="hidden">
</form>
</div>
]]></cmd>
</ajax>