Sometimes you might need to download a live SSAS database into a Visual Studio project. Like if someone build an SSAS solution and then deleted the development project.
Here's an explanation on how to do it:
How to: Create an Analysis Services Project Based on an Existing Analysis Services Database
http://msdn.microsoft.com/en-us/library/ms365361(SQL.90).aspx
(Short version: File -> New project -> Import Analysis Services 2008 Database template)