You'll probably have an issue opening and closing the LI in different areas of the xslt. But there's a way to solve that, too. In fact, you can see an example of the whole solution, including the "position() mod " in the Runway Gallery module.

The relevant bit of xslt from the gallery module is:

<xsl:param name="currentPage"/>

<xsl:variable name="imagesPerRow" select="4"/>



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<xsl:template match="/">

    <!-- a little hack to work around the xslt syntax checker when
opening/closing UL lists in two separate IF statements -->

    <!-- if it weren't for IE we could use a single UL and simply float the LI's and they'd auto-wrap -->

    <!-- but for IE we either need separate UL rows or else we need to hard-code the LI's height in CSS -->

    <!-- this approach with separate UL rows works in all browsers and row heights -->

    <xsl:variable name="ulOpen"><xsl:text>&lt;ul
class="runwayGallery"&gt;</xsl:text></xsl:variable>

    <xsl:variable name="ulClose"><xsl:text>&lt;/ul&gt;</xsl:text></xsl:variable>



    <xsl:for-each select="$currentPage/node [string(data [@alias='umbracoNaviHide']) != '1']">

        <!-- open a row of images -->

        <xsl:if test="position() = 1 or position() mod $imagesPerRow = 0">

            <xsl:value-of select="$ulOpen" disable-output-escaping="yes" />

        </xsl:if>



        <!-- display each image in the row, with the count of photos in each gallery -->

        <li>

            <a href="{umbraco.library:NiceUrl(@id)}">

                <img src="{concat(substring-before(./node/data [@alias='umbracoFile'],'.'), '_thumb.jpg')}"/>

                <br />

                <b><xsl:value-of select="@nodeName"/></b>

            </a>

            <br />

            <xsl:value-of select="count(./node)"/>

            <xsl:text> Photo</xsl:text>

            <xsl:if test="count(./node) &gt; 1">

                <xsl:text>s</xsl:text>

            </xsl:if>

        </li>



        <!-- close the row of images -->

        <xsl:if test="position() = ($imagesPerRow - 1) or position() mod ($imagesPerRow - 1) = 0 or position() = last()">

            <xsl:value-of select="$ulClose" disable-output-escaping="yes"/>

        </xsl:if>

    </xsl:for-each>



</xsl:template>



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cheers,
doug.