question about apply-templates / following-sibling

I would like to update some XML documents by inserting an element.
The documents are vaild to the DocBook DTD, but the following is a
simple subset which shows the problem I have:

<!ELEMENT chapter
    (   beginpage?, chapterinfo?, title
        (index)*,
        (
          (
            (para | %chapter.elements; | beginpage)+,
	  (section* | simplesect*)
          )   |
	(section+ | simplesect+)
        ),
        (index)*,
    )
>

<chapter>
  <beginpage pagenum="1">
  <title>test</title>
  <index>index stuff</index>
  <index>index stuff</index>
  <para>text1</para>
  <beginpage pagenum="2">
  <!-- the new para should be here -->
  <index>index stuff</index>
  <index>index stuff</index>
</chapter>

<xsl:template match="chapter">
   <xsl:copy>
      <xsl:apply-templates select="@*"/>
      <!-- copy everything before new para, including index elements -->
      <para>New para</para>
      <!-- copy everything after new para, including index elements  -->
   </xsl:copy>
</xsl:template>