whats sp_xml_preparedocument ?
SP_xml_prepareDocument is an extended proc that uses the MSXML Parser
and parses the document and creates a in memory tree like structure
of the XML and returns a integer what can be assumed as pointer value.
This is further used in OPENXML statement to read the values from
various nodes using the pointer and the XPath
this article explains briefly how to use SP_XML_PREPAREDOCUMENT to
parse an XML