Victoria Yudin has a great piece up covering reporting on Extender Data in Dynamics GP. Extender is allows custom fields without having to write customizations but it’s a pain to report off of so it’s nice to see Victoria tackle this subject.
Reporting on Extender Data in Dynamics GP
Archived post from 2008. Dynamics GP and the links it points to have changed since; check current documentation before relying on version-specific steps.