figured it out -- thought i'd post it here in case anyone was curious.
in categories.php, the code read:
      
	Code:
	if ($short_list) {
		$to_search = "$sql_tbl[categories].categoryid,$sql_tbl[categories].parentid,$sql_tbl[categories].categoryid_path,$sql_tbl[categories].category,$sql_tbl[categories].product_count,$sql_tbl[categories].avail,$sql_tbl[categories].order_by";
	} else {
		$to_search = "$sql_tbl[categories].*";
	}
 
i added the field i needed (description) to the SQL statement like this:
        
	Code:
	if ($short_list) {
		$to_search = "$sql_tbl[categories].categoryid,$sql_tbl[categories].description,$sql_tbl[categories].parentid,$sql_tbl[categories].categoryid_path,$sql_tbl[categories].category,$sql_tbl[categories].product_count,$sql_tbl[categories].avail,$sql_tbl[categories].order_by";
	} else {
		$to_search = "$sql_tbl[categories].*";
	}
 
this then allowed me to use 
	Code:
	{$categories[cat_num].description}
 
in my categories.tpl