Hi there, give this a try:

<xsl:template match="/">
    <ul>
      <xsl:for-each select="$currentPage/descendant-or-self::node [string(data [@alias='umbracoNaviHide']) != '1']">
        <li>
            <xsl:attribute name="class">
                <xsl:if test="$currentPage/@id=@id">
                    <xsl:text>active</xsl:text>
                </xsl:if>
            </xsl:attribute>
            <a href="{umbraco.library:NiceUrl(@id)}"><xsl:value-of select="@nodeName"/></a>
        </li>
      </xsl:for-each>
    </ul>
</xsl:template>

HTH,
Nik