From where do my cubes get their data?

SQL Server Analysis Services 2005 cubes may get their data from a variety of sources, including the following:

SQL Server 7.0/2000/2005 (including SSAS 2005)
Oracle 9.0 (x86 only)
IBM DB2 8.1 - only available for SS 2005 Enterprise Edition or SS 2005 Developer
Access with Microsoft Jet 4.0 OLE DB provider (x86 only)
Teradata v2R6 (x86 only).

More details available here.

In addition to having the ability to obtain data from a variety of sources, SSAS 2005 has an abstraction layer. This abstraction layer was not available in earlier versions of SSAS. The abstraction layer is developed as a data source view. A data source view is a logical data model of one or more data sources. Some of the items that may be included in a data source view include tables, named queries, relationships, and named calculations. Even more, the data source view may contain items originating from multiple data sources.

More details available here.