</Form local="true">
 <Gitems>
   <Items><Type mytype="true">Text<Type><Name>t1<Name> .... <Items>
   <Items><Type>But<Type><Name>b_ok<Name> .... <Items>
 </Gitems>
 <Gitems>
   <Items><Type mytype="true">But<Type><Name>b_c<Name> .... <Items>
 </Gitems>
</Form>

<?xml version="1.0" encoding="windows-1251" ?> 
 <xsl:stylesheet xmlns:xsl="http://www.w3.org/1999/XSL/Transform" version="1.0">
 <xsl:output method="xml" encoding="windows-1251" />

<xsl:template match="/ | @* | node()">
    <xsl:copy>
      <xsl:apply-templates select="@* | node()"/>
    </xsl:copy>
</xsl:template>


<xsl:template match="Items">
 <xsl:choose>
  <xsl:when test="Type/@mytype"> 
    <!-- здесь спец обработка -->
  </xsl:when>
  <xsl:otherwise>
   <xsl:copy>
      <xsl:apply-templates select="@* | node()"/>
   </xsl:copy>
  </xsl:otherwise>
 </xsl:choose>
	
</xsl:template> 

</xsl:stylesheet>