In light of the GP 2010 and Office 2010 launches, Inside Microsoft Dynamics GP take a look at Microsoft Dynamics GP Combined with Microsoft Office and SharePoint.
GP 2010 + Office 2010 + Sharepoint
Excel & OfficeGP 2010
Archived post from 2010. Dynamics GP and the links it points to have changed since; check current documentation before relying on version-specific steps.