The first part is a little work. You could import the data one column at a
time from the old table to the new one. Below is an example of such a query.

INSERT INTO TheOldTable ( Customer, GP_Date, GP_Amount )
SELECT TheNewTable.Customer,
 #6/1/2006# AS GP_Date,
 TheNewTable.[July 06 GP]
FROM TheNewTable;

After running it would would have to change the date within the #'s to that
of the matching field. For example the above is #6/1/2006# and [July 06 GP].
You would need to change them to #7/1/2006# and [August 06 GP].

Also I noticed in another post that you were going to name a field in the
new table "Date". Date is a reserved word and you might run into trouble with
using it. That's why I suggested something like GP_Date instead.

As for the second part, you are probably still grouping by the date field.
Try changing it from Group By to Where. The resulting SQL should look
something like this:

SELECT jenniferspnc2.Customer,
 Sum(jenniferspnc2.GP_Amount) AS SumOfGP_Amount
FROM jenniferspnc2
WHERE (((jenniferspnc2.GP_Date)>DateAdd("yyyy",-1,Date())))
GROUP BY jenniferspnc2.Customer;