Hi Karl,
  Please try this XSL..

<?xml version="1.0"?>
<xsl:stylesheet xmlns:xsl="http://www.w3.org/1999/XSL/Transform"
version="1.0">

<xsl:output method="xml" indent="yes" />

<xsl:variable name="file2" select="document('file2.xml')" />

<xsl:template match="/bookshelf">
   <bookshelf>
     <xsl:copy-of select="*" />
     <xsl:copy-of select="$file2/bookshelf/*" />
   </bookshelf>
</xsl:template>

</xsl:stylesheet>

Regards,
Mukul

http://gandhimukul.tripod.com