difficult pivot?

hi!

for a pivot view in our project database i need to join two tables.

table bills
----
customer_id project_id month year price

table payments
----
customer_id month year payment

desired result
----
customer_id project_id month year price payment

desired example:
customer 2 is participating in project 2 & 3. - payment should be equal in line 2 and 3.
----
row 1: 1 2 1 2006 0 300
row 2: 1 2 2 2006 1,000 500
row 3: 1 3 2 2006 150, 500
row 4: 1 2 3 2006 750 0

if i use the code below i always miss line 1 because there is no entry for the second table. of course not, [...]

SELECT customer_id, project_id, month, year, price, (SELECT price FROM bills WHERE bills.customer_id=payments.customer_id AND bills.month=payments.month AND bills.year=bills.year) FROM payments

i didn't figure out how to solve that in access. - i know it would be easier in a stored procedure, though, do you have an idea to solve my gordian knot?

cheers