Using php next to Category descriptions

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I'm trying to run a block of PHP code on the category descriptions page. I set this to be the categories description but it doesn't seem to execute, it just displays it instead. Can anyone help? Here is the code:

<?php  
 if ($featured_products->RecordCount() > 0) {
   for ($i = 0; $i < $featured_products->RecordCount(); $i++) {
   echo '<div class="categoryListBoxContents" style="width:33%;">';
   echo '<a href="' . zen_href_link(FILENAME_DEFAULT, 'main_page=product_info&products_id=' . $featured_products->fields['products_id']) . '">';
   echo zen_get_products_image($featured_products->fields['products_id']);
   echo '</A></div>';     
} 
} ?>