The First Answer From Sqillman (http://serverfault.com/a/506567/173328) works! Kudos!
Here's what it solved for us...
For us, the answer (above/below?) allows access to SQL Server 2000 databases from SQL Server 2012 Integration Services packages that are hosted on a SQL Server 2012 database server running on Windows Server 2012 OS. We followed these suggestions to install SQLNCLI10 on our 2012 database server. Our problem occured because the hosting db server never had the old SQL 2008 "SQLNCLI10" installed. That is, it never had SQL Server 2008 installed or an older OS.
The SSIS server error that started our research was: "The requested OLE DB provider SQLNCLI10.1 is not registered"
It is worth noting that when following the solution from squillman/technet/etc, while installing the 2008 SQLNCLI.msi on one of our new servers, we received the error "Installation of SQL Server 2008 failed because a higher version already exists on the machine...." Despite this, the driver was installed and worked properly without hurting 2012 db server functionality. It installed alongside the existing 2012 SQLNCLI11 driver nicely.
In SSIS 2012, our packages use an "OLE DB\SQL Server Native Client 10.0" connection to access the SQL Server 2000 databases (we actually just edited the connection strings and changed Provider from "SQLNCLI11.1" to "SQLNCLI10.1"). The developers had both drivers on their machines and so did the db servers we originally deployed to. It was only when the final "Pure" 2012 servers were built out that the old driver disappeared and packages failed.
Note: In connection strings, "Provider = SQLNCLI10.1" is a synonym for "Provider = SQLNCLI10". they both use the same dll.
-Patrick Hayes, Stefanini