A select distinct sum problem

Hey all.

I need to do a select and I didn't find how to do it yet.

The structure of the table:

table product_mov
idmov
idproduct
date
in
out
average

Example of data in the order of fields. I'll put the product name into
() to easier view.

1 - 2 (Memory) - 2007-06-10 - 10 - 0 - 10
2 - 2 (Memory) - 2007-06-11 - 0 - 5 - 5
3 - 3 (CPU) - 2007-06-11 - 20 - 0 - 20
4 - 2 (Memory) - 2007-06-12 - 13 - 0 - 18
5 - 3 (CPU) - 2007-06-15 - 0 - 3 - 17

What I have to do is to return the sum of the average of all products
lower than a date. But I need to sum only the register immediately
lower than the date of each product.

So, if I want the average sum of the day 2007-06-16, I'll take the
last memory and cpu registers and sum it.
In this case the registers 4 and 5. My result will be 18+17 = 35.

If I want of the day 2007-06-13, I'll take the registers 4 and 3 and
sum it. 18+20 = 38

How can I do that?

--
Kico Zaninetti
carpe diem