Leslie Vail now has her Dex.ini switch document available to download. Go get this. The Dex.ini file can be positively magical when it comes to tuning how Dynamics GP loads.
Dex.ini switches for Dynamics GP now available to download
Install, Upgrade & AdminDevelopment & Integration
Archived post from 2010. Dynamics GP and the links it points to have changed since; check current documentation before relying on version-specific steps.