Microsoft makes it official. Microsoft announces Microsoft Dynamics GP 2013 planned availability of December 19, 2012
Microsoft announces Microsoft Dynamics GP 2013 planned availability of December 19, 2012 – Inside Microsoft Dynamics GP – Site Home – MSDN Blogs
Microsoft & the GP EcosystemGP 2013
Archived post from 2012. Dynamics GP and the links it points to have changed since; check current documentation before relying on version-specific steps.