Pivot table XL2007: calculate difference between 2 columns
 

I have some data in the format:
Name Year Sale$
Jill 2008 15
Jill 2008 29
Mike 2008 12
Mike 2008 53
Jill 2009 24
Jill 2009 43
Mike 2009 17
Mike 2009 26

Pivot table is set up as:
2008 2009
Sum of Sales$ Sum of Sales$
Jill 44 67
Mike 65 43

(in reality, there are several columns under 2008 and 2009, showing other
performance data as well)

Now I want to show a year-to-year comparison; a calculated column that would
show:

2008 2009 Annual
Sales$ Sales$ Change
Jill 44 67 23
Mike 65 43 (22)

I can do this with calculated columns when the source data is all from
different columns, but I haven't figured out how to do it across multiple
pivot table columns that pull from the same source data column and are just
differentiated by a higher-order split, in this case, year.

Is this possible in Excel2007, and if so, can someone provide some direction?

Many thanks,
Keith