Muchisimas gracias wiwi74 por tu pasiencia, eres el mejor.
el codigo me quedo asi:
Código PHP:
<?php
header("Content-type: text/xml");
$dom = new DOMDocument();
$dom->load('test.xml');
$rows = $dom->getElementsByTagName('row');
echo '<?xml version="1.0" encoding="UTF-8"?>';
echo '<chart><title>Test</title><subtitle>';
echo $rows->length;
echo '</subtitle><name_value1>habitantes</name_value1><type>bars</type><header_height>80</header_height>';
echo '<chart_data>';
$contar = array();
foreach($rows as $row){
$name = $row->getAttribute('name');
$value = $row->getAttribute('value');
$contar[$name] += 1;
}
foreach($contar as $nombre => $cantidad){
echo '<piece>';
echo '<name>'.$nombre.'</name><value1>'.$cantidad.'</value1>';
echo '</piece>';
}
echo '</chart_data>';
echo '<colours><colour>0xaff500</colour><colour>0x3699a9</colour><colour>0xdaa000</colour><colour>336699</colour></colours>';
echo '</chart>';
?>