SQL Server 2005 has been released to manufacturing today. The public launch date is November 7. My understanding is that Great Plains SP4 will support SQL Server 2005. Do you want a free copy of SQL Sever 2005? Visit a launch event and get a free copy of SQL Server 2005 and Visual Studio 2005.
SQL Server 2005 Released to Manufacturing
SQL & DataInstall, Upgrade & AdminSales, Purchasing & Inventory
Archived post from 2005. Dynamics GP and the links it points to have changed since; check current documentation before relying on version-specific steps.