If you want a quick tutorial on using Excel or Excel Services with SQL Server Analysis Services 2008, there is a nice one up on the Excel team blog. It’s not terribly in depth but it does give a nice starting point if you’re just getting started.
Excel and Excel Services with Analysis Services 2008
Archived post from 2008. Dynamics GP and the links it points to have changed since; check current documentation before relying on version-specific steps.