I think I need to use the SUMPRODUCT function but need help w/ the formula.

Using the following data:
Investor Name Payment Due Date Payment Amount
Sue 01/01/07 $10
Charlie 09/01/08 $20
Fred 12/08/08 $100
Charlie 01/01/06 $50
Fred 09/16/07 $100
Sue 10/01/08 $75
Sue 12/15/08 $100

I need the formula to find all payments for each investor and total only the
ones that are due later than 08/01/08. So the result should show:

Sue - $175
Charlie - $20
Fred - $100

thanks!