calculate sales based on specific dates in table in sql server 2000

Hi all.

I have a SQL Server 2000 table (myTableA) that has the following fields: ContractNo, CustomerID, StartDate, EndDate

I have another table (myTableB)that stores every sales transaction for each customer. One of the fields in myTableB is InvoiceDate. I want to be able to sum up all the sales based on the InvoiceDate falling between the StartDate and EndDate for the customers' contractNo.

So for example, let's say I have in myTableA:

ContractA---Customer123---01/01/2010---03/01/2010
ContractB---Customer123---03/02/2010---12/31/2010

And in myTableB:
Customer123---InvoiceDate:02/01/2010---$5
Customer123---InvoiceDate:02/24/2010---$5
Customer123---InvoiceDate:03/05/2010---$20

I would like the end result to show:
ContractA---Customer123---$10
ContractB---Customer123---$20

How can I do this?

Thank you in advance!