In a pivot table that has just two rows of data I would like to
calculate the difference between the two rows (row1 - row2) for all
the columns.

One thing I tried was to select a cell in the Grand Total row, right
click and select Value Field Settings then enter Custom Name "Diff".
Then in the Show Value As tab, select Difference From and "row1" and
ok.
the data in rwo1 is now blank, row2 is is not what I expect and the
grand total is blank.

So I apparently dont have a clue about this and need to be pointed in
the right direction.

Excel 2007
Plot row differences.
Two ways.
http://www.mediafire.com/file/mommwnenzvm/11_02_09.xlsx