In his new post on International ACH Transaction (IAT) functionality for Microsoft Dynamics GP 10.0, MVP Mariano Gomez gives us some information on improved international ACH functionality due in the soon to be released Service Pack 4.
International ACH Functionality for Dynamics GP 10
Off-Topic & MiscellaneousGP 10
Archived post from 2009. Dynamics GP and the links it points to have changed since; check current documentation before relying on version-specific steps.