We finally installed an instance of ArcSDE 10 today. My first attempt at connecting in ArcCatalog 9.3.1 failed with the following error: Failed to connect to the specified server. This release of the GeoDatabase is either invalid or out of date. [Please run the ArcSDE setup utility using the -o install option.] DBMS table not found [sde.sde.GDB_Release]  Turns out the solution was simple, this article points out that Service pack 2 is required.