si probas con xpath ?
http://codepad.org/Z9VIH0f6
Código PHP:
Ver original<?php
$XML_STR = <<<EOL
<xdm:Device xmlns:xdm="http://www.hp.com/schemas/imaging/con/xdm/1.1/" xmlns:dd="http://www.hp.com/schemas/imaging/con/dictionaries/1.0/" xmlns:bsi="http://www.hp.com/schemas/imaging/con/bsi/2003/08/21" xmlns:wsdl="http://schemas.xmlsoap.org/wsdl/" xmlns:count="http://www.hp.com/schemas/imaging/con/counter/2006/01/13" xmlns:media="http://www.hp.com/schemas/imaging/con/media/2006/01/13" xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance" xmlns:pwg="http://www.hp.com/schemas/imaging/con/pwg/sm/1.0/">
<xdm:Information>
<xdm:Component id="iSystem" componentType="system">
<dd:MakeAndModel>HP Color LaserJet CM6030 MFP</dd:MakeAndModel>
<dd:Description>BUSINESS 505549 E4 P2</dd:Description>
<dd:ProductNumber>CEXXX</dd:ProductNumber>
<dd:Manufacturer>
<dd:Name>HP</dd:Name>
</dd:Manufacturer>
<dd:SerialNumber>ETETCD4744</dd:SerialNumber>
<dd:ServiceID>22013</dd:ServiceID>
<dd:Version>
<dd:Revision>52.132.6</dd:Revision>
<dd:Date>2011-02-15</dd:Date>
</dd:Version>
<dd:MopierFunctionSetting>Enhanced</dd:MopierFunctionSetting>
<dd:AutomaticResourceSaving>Automatic Resource Saving Enabled</dd:AutomaticResourceSaving>
</xdm:Component>
<xdm:Component id="iMarkingEngineController" componentType="board">
<dd:BoardTypeEnum>markingEngineControl</dd:BoardTypeEnum>
<dd:Description>marking engine controller</dd:Description>
<dd:Version>
<dd:Revision>PKauai 54</dd:Revision>
</dd:Version>
</xdm:Component>
<xdm:Component id="iFormatter" componentType="board">
<dd:BoardTypeEnum>systemControl</dd:BoardTypeEnum>
<dd:Description>formatter</dd:Description>
</xdm:Component>
</xdm:Information>
</xdm:Device>
EOL;
//$xml = simplexml_load_file("test.xml");
$results = $xml->xpath("/xdm:Device/xdm:Information/xdm:Component[1]/dd:MakeAndModel");
foreach ($results as $result) echo "$result\n";