Crosstab query with rolling dates

[jim]

I have a table with 3 fields:

Charge Incurred Date
Charge Paid Date
Charge Amt

I have created a crosstab query which sums the charge
amount by paid month(rows) for the previous 36 months and
pivots the paid month by the incurred month. The query is
working fine except I now want to pull all incurred months
older than 36 months into the 1st bucket for each paid
month.

i.e.

For paid month May, 2003, I get a separate column for each
of the 36 months prior to May, 2003(June, 2000 - May,
2003) showing when all charges have been incurred. I want
to take all incurred charges prior to June, 2000 and add
them into the June, 2000 amt. I do not want to show
columns for any months beyond the 36 I already have.

Any suggestions?

Thanks,
Jim