By the way...in this instance I don't see why you cannot do this very easily by running a CSV report now. And then running the same report later and merging the two.
Create a CSV report that has two fields:
Computername, Bytes Total
machine1, 256 MB
machine2, 384 MB
etc...
Then do the same report after the upgrade.
Computername, Bytes Total
machine1, 512 MB
machine2, 1024 MB
etc...
Now open both csv file in excel, and copy the Bytes Total column from the second report to the first report. Add a subtraction in the fourth column.
Computername, Original Bytes Total, New Bytes Total, Difference
machine1, 256 MB, 512 MB, 256MB
machine2, 384 MB, 1024 MB, 640MB
etc...
Now you have all you data in excel and you can do any of the pretty excel charts you want.
