How to retrieve subtotal for order lines (rollup does not exist in sql 2000)
Figured it out:

select TS.Order_no, part_no, cost_per_line, 
       case when Order_no = (select top 1 Order_no from #tempsales 
                           where cust_po = TS.cust_po
                          order by Order_no asc)
            then (select sum(cost_per_line)
                     from #tempsales
                     where Order_no &lt;= TS.Order_no
                        and cust_po = TS.cust_po)
            else '0' end as 'Sub Total',
       case when Order_no = (select top 1 Order_no from #tempsales 
                           where cust_po = TS.cust_po
                          order by Order_no asc)
            then (select CAST(ROUND(SUM(cost_per_line), 2, 1) AS DECIMAL(18, 2))
                      from #tempsales) 
             else '0' end as 'Grand Total'
from #tempsales TS