I apologize if this is a repeat.

I am trying to compare a monetary value from one column to another column.
However, I am running a worksheet with auto-filters because I have quite a
bit of data including every line item from a 76 page invoice. I am trying to
find the difference between different months and years. For example, I want
to compare the total of one line item from July 2008 to the same line item in
July 2009. But then lets say I want to be able to compare the same line item
from July 2008 to July 2007. However, I want to be able to filter out
everything but that one line item. I want to be able to do this for every
single line item (rows) and for all and individual months(columns). I hope
this makes sense. Can anyone help me write a formula? Obviously, I'm not
very proficient at Excel. I have Excel 2003. Please help!