Mohammad Daoud has a nice look at Audit Trails in Dynamics GP. I have to say though that I still prefer FastPath for audit trails in Dynamics GP. As a customer I bought FastPath over the GP Audit Trail product and I would do it again without reservation.
Audit Trails in Dynamics GP
Archived post from 2010. Dynamics GP and the links it points to have changed since; check current documentation before relying on version-specific steps.