I'm making a couple of assumptions he

If you've got details of your items in column B, with the relevant dates in
column A
(cells A1:B7):
01/02/2007 3
01/02/2007 8
01/02/2007 2
01/05/2007 1
01/05/2007 5
01/06/2007 3
01/06/2007 6

Then in column D you've got a list of unique months
(cells D1:D3):
01/02/2007
01/05/2007
01/06/2007

You could use the following formula in cell E1 to give you a sum of items
appearing in each month:
{=SUM(IF(D1=$A$1:$A$7,$B$1:$B$7))}

This has to be entered as an array formula - press Ctrl~Shift~Enter instead
of just Enter when completing the formula. Drag this down from E1 to E3 for
your totals on each month.

Regards,