Here's a starter ... the following XSLT stylesheet will order your XML based on NICKID:

<?xml version="1.0" encoding="ISO-8859-1"?>
<xsl:stylesheet version="1.0"
 xmlns:xsl="http://www.w3.org/1999/XSL/Transform">

<xsl:output method="xml" version="1.0"
 encoding="iso-8859-1" indent="yes"/>

<xsl:template match="MEMBERLIST">
 <xsl:apply-templates select="LIST">
  <xsl:sort select="NICKID" data-type="number" order="ascending" />
 </xsl:apply-templates>
</xsl:template>

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

</xsl:stylesheet>
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