I need to add values in different columns of data based on due dates.

Categories of data include:
Current Due Date (say, 2/1/09)
Grace Days (i.e., 5 days)
Current Payment Amount
Jan Due Date (1/1/09)
Jan Payment Amount
Dec Due Date (12/1/08)
Dec Amount

The current payment amount falls into a "Within Grace Days" column if it is
within 5 days of the current due date. I need to lump amounts due for "1-30
Days", "31 to 60 Days", etc. based on the amounts and when the payments were
due.

As today's date changes, the data will need to flow into the respective
delinquency categories as it passes from 30 to 31 days, etc.

I would like to copy this formula down the page and need to use an ISNA or
ISBLANK formula (say they don't owe a Jan or Dec payment) as I don't want a
$0.00 amount in a cell - it needs to stay blank.

Your help is greatly appreciated.