In my first example it will come up with the months as columsn

truncate table #invoices

insert into #invoices (invoiceid, invoicedate, invoicetotal, salesperson, clientid)

select 1, cast('2008-1-15' as datetime), 200, 1, 1

union all

select 1, cast('2008-2-15' as datetime), 100, 1, 1

union all

select 1, cast('2008-3-15' as datetime), 150, 1, 1

union all

select 2, cast('2008-1-15' as datetime), 1200, 2, 1

union all

select 2, cast('2008-2-15' as datetime), 1100, 2, 1

union all

select 2, cast('2008-3-15' as datetime), 1150, 2, 1

select salespersons.salesperson, #month.[month], sum(i.invoicetotal) totaal

from #month, (select distinct salesperson

from #invoices) salespersons, #invoices i

where i.salesperson = salespersons.salesperson

and #month.[month] = datepart(month, i.invoicedate)

group by salespersons.salesperson, #month.[month]

if you use the same tables and execute this query it will come up with month / salesperson / sum(invoices) per salesperson and month... I am not familiar with SSRS so i cannot help you with that.