table cell with in a table cell

Hey guys....

Im trying to do some work with tables in my XSL FO document.  I have a requirement to have a column in a table that can hold up to 4 different data results.  So i thought i could have children table cells with in my parent table cell but when i render this in PDF it doesnt happen.

Heres the snippet of code im using :

<fo:table-cell>
         <fo:table-cell padding="6pt" border="0.5pt solid black">
                <fo:block background-color="grey"> N </fo:block>
         </fo:table-cell>
         <fo:table-cell padding="6pt" border="0.5pt">
               <fo:block background-color="white"> A </fo:block>
         </fo:table-cell>
</fo:table-cell>

so im wondering is there a better way to do this.  Im new to xsl fo, so any help would be appreciated.

Tom.