Macbook- having problems opening itunes

Hi,

I recently tried to update my Macbook (2009) to a new version of OSX. For whatever reason, the update did not work and my Mac didn't work for 5 days. I ended up having to reinstall my initial program disks. When I did that, I lost my Pages, Keynote, and Numbers. I also lost the ability to open Itunes. When I click on itunes, it has a white circle with a slash through it and says "You have Mac OS X 10.6.3. The application requires Mac OS X 10.6.8 or later."

Any help as to how to redownload/reinstall Itunes would be greatly appreciated.

Thanks!