In Touch with Dynamics (GP) digs into at How to create 32 bit ODBC data sources for Dynamics GP from a 64 bit server.
In Touch with Dynamics (GP): How to create 32 bit ODBC data sources for Dynamics GP from a 64 bit server.
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Archived post from 2011. Dynamics GP and the links it points to have changed since; check current documentation before relying on version-specific steps.