This OLE DB Provider is provided by Microsoft.
Include "Provider=Microsoft.Project.OLEDB.11.0" in the connection string to use this provider.
There is no 'Microsoft Project 2003 OLE DB' installation package to download. (if you know about an installation package URL you can contribute to the community by submitting the info to us through this message form)
The Microsoft Project 2003 OLE DB provider can be used to connect to the following data sources by using the following connection string references: