I am using excel, on XP 2003 SP2 (might be 3)

I am trying to add amounts together using several criteria. I have a column
called "sales type" (of which there are many types) I then have a column of
the month they are paid (Jan, Feb, Mar, etc.etc.)

I want to show in a cell the sales value of a "sales type" in a given
"month" using a formula instead of selecting each cell manually and adding it
to a simpl addition sum string.

Any help much appreciated!