METS/XML Search facility

I'm trying to write an XML Document search engine specifically for METS encoded data ( http://www.loc.gov/standards/*mets*/ ). I've tried knocking together some proof of concept code in PHP4 using both DOM and xml_parser but I've run into dificulties with both. Can anyone point me at some code/class which enables me to search within an XML document for the existance of $string within a set list of tags eg. <METS:title>Some Title Here</METS:title> <METS:description>This is a description of this document</METS:description> It seems like a very straightforward task. -- Dan Field <dof@llgc.org.uk> Support Programmer: Cymru ar y we / Wales on the Web cy_GB: http://www.cymruarywe.org en_GB: http://www.walesontheweb.org