This is possible but not by default in InfoPath.
Since InfoPath has no way of storing the old values you would either need to
keep previous version of the document or have the data stored externally.
Using the Database Accelerator from http://www.qdabra.com you can enable
version history as it is stored in SQL and I have several examples where even
field level tracking is done.
SharePoint Libraries can have version history as well.
In theory you could add extra fields to your form and manage saving x
previous values if you really wanted to.

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Thanks
Clay Fox
Qdabra Software
http://www.qdabra.com
InfoPathDev.Com
The Largest InfoPath Forum in the World
http://www.infopathdev.com
> Is there a way enable Track Changes in InfoPath 2007? I have a form where
> some numbers are changed occasionally and we would like to be able to see
> what the previous number was in a particular Field. Is there a way to do
> that?
> Thanks