[Shuchi Shrivastava]

The complete functional content would be available as a separate download.Meanwhile, before installing the CS6 Functional content, backup your 5.1 content to a safe location and if you already have 5.1 content you could point the CS6 library to its location.

If your 5.1 is deleted while installing 6.0 content – copy the cs6 library from C:Program FilesAdobeAdobe Encore CS6Library and place it at another loacation and rename it.
Now uninstall the CS6 Content and reinstall the 5.1 FC using the disc or the downloded FC you have. In this way you will recover back your 5.1 FC and can also use the 6.0 FC by pointing Encore to its location. I tried it and this works.

And this problem will no longer be faced once the downloadable full version of CS6 FC will be available