Count formula in a search

Hi

I would like to create a saved search that counts the total number of opportunities created in a month by lead source, for each of my departments.  Departments are tracked on the opportunity

so the result in the search is something like:

Source                        Depart 1               Depart 2       Depart 3

Web                               5                         10              0
Phone                             3                          23             45
Undefined                         1                         100            2

the formula needs to be something like

summary type: sum

Formula  - case when (department) = Depart 1 then count(number) else 0 end

can anyone help??

Thanks