I came across an issue today where a website had a dependency on the SQL Server Native Client 10.0, which is part of SQL Server 2008. A recent upgrade to SQL Server 2012 caused SQL Server Native Client 11.0 to be installed and version 10.0 to be uninstalled.
Different versions of the Native Client can be installed side-by-side, and fortunately there is also a redistributable installation. The documentation shows the redistributable located at %CD%\Setup\ on the installation disk. That is great if you have the installation disk handy. Many of us have data centers located remotely from our offices so instead we have an authorized repository of the installation media located on a network drive.
I searched and searched for sqlncli.msi, the redistributable for Native Client without success on the SQL Server 2008 R2 media, the previous version installed for this website. Finally I went to the SQL Server 2008 media and still was unable to find it in the Setup folder. I was finally able to locate it in the \x64\Setup\x64 folder, though.
Once I had the sqlncli.msi file, it started up a wizard with a few simple screens and I was able to get this installed side-by-side with SQL Native Client 11.0. The website dependency started operating properly again and I was able to confirm the installation of the Native Client drivers.
Hopefully this post will save you some time if you come across this issue. The full documentation is located on TechNet: http://technet.microsoft.com/en-us/library/ms131321%28v=sql.105%29