Do ADO MD.NET and XMLA clients communicate differently with a SQL Server 2000 Analysis Services instance than with a SQL Server 2005 Analysis Services instance?

Yes. An Analysis Services 2005 or 2000 instance must be able to listen to and receive XMLA requests to communicate with ADO MD.NET or XMLA clients. Because all roads that lead to Analysis Services 2000 go through Pivot Table Service, the XMLA software development kit (SDK)—an Internet Server API (ISAPI) extension DLL—is required for the server to receive XMLA requests. However, in Analysis Services 2005, XMLA is the native communication mechanism. ADO MD.NET clients can communicate over XMLA using a binary transfer mechanism (by specifying Datasource=<server> on the connect string) and non-ADO MD.NET clients can communicate using an HTTP access module (by specifying Datasource=http://<server>).