The SQL Server OLE DB provider and ODBC driver, plus associated network libraries, are part of MDAC (Microsoft Data Access Components) for SQL Server 2000 and earlier. At least MDAC 2.6 is required for accessing SQL Server 2000. Since Windows 2000, MDAC is part of the operating system. Windows 2000 shipped version 2.5 so requires updating to access SQL Server 2000. Windows XP SP2 ships the latest redistributable version 2.8 SP1. Windows Server 2003 SP1 ships with MDAC 2.8 SP2 which is not available separately. Basically, on Windows XP or later you don't need to install extra software to access SQL Server 2000 or earlier. The .NET Framework implements the SQL Server access protocol natively, but requires the network libraries from MDAC. You can access SQL Server 2005 using the SQLOLEDB provider for ADO/OLE DB, SqlConnection from .NET 1.1, and the SQL Server ODBC driver. However, the old provider does not support many new features of SQL Server 2005. To get full functionality, you need to install and use SQL Native Client (for ADO/OLE DB/ODBC), or use .NET Framework 2.0 or later. For ADO/OLE DB, specify SQLNCLI rather than SQLOLEDB. For ODBC, use the 'SQL Native Client' driver rather than the 'SQL Server' driver.
Stability. What an interesting concept. -- Chris Maunder