> The approach I've considered has been to use <xsl:for-each 
> select="row"> to
> cycle over each row, and then <xsl:for-each 
> select="col[2]/data"> to cycle
> over each <data/> in the second column ... but how do I then 
> reference the
> corresponding nth child of col[3]? 

<xsl:variable name="p" select="position()"/>
<xsl:value-of select="ancestor::row/col[3]/data[$p]"/>

Michael Kay
http://www.saxonica.com/