I've tried your suggestion but it didn't seem to affect the order
unfortunately. :(

    <xsl:template match="Item">
        <xsl:choose>
            <xsl:when test="key('val', @ID)">
                <li><xsl:value-of select="@title"/></li>
                <ul>
                  <xsl:apply-templates select="key('val', @ID)">
                    <xsl:sort select="@order" data-type="number"/>
                  </xsl:apply-templates>
                </ul>
            </xsl:when>
            <xsl:otherwise>
                <li><xsl:value-of select="@title"/></li>
            </xsl:otherwise>
        </xsl:choose>
    </xsl:template>

	Martin Honnen
	http://msmvps.com/blogs/martin_honnen/