Macro for addition

Hi all,
I need some help for the following (should be easy for most of you)

In column A, I have numbers. in column B, C... have more prices.
I want - for each modification of values in column A - to do the Summary of the values in Cell in "B" and that summary

Exemple :
- From Cell A1 to A10, value = 1.00
I want in Cell D10, the summary of Cells B1 to B10
- From Cell A11 to A25, value = 1.20
I want in Cell D25, the summary of cells B11 to B25
and so on

PS: I do not know te different value in column "A"
Thanks in advance
Herve

Steve,
that is right,
For each change of value in A I want the Sum of B in cell D.

Steve, this was exactly was I wanted
cheers