Microsoft has put developers on notice that it is deprecating the ADO.NET provider for Oracle shipped with the .NET Framework: System.Data.OracleClient (OracleClient) as of .NET 4, expected in 2010.

You'll also need to install Oracle's ODP.NET_Managed_ODAC package. As much as I'd like to pretend that I'm all-knowing but this information comes from Yonayli ...