It is possible to install the Cartes du Ciel-SkyChart version 3.0 over a full Windows version 2.76 in the same directory, and run the Cartes du Ciel-SkyChart 2.76 version apart from the 3.0 version. But you can also install the 3.0 version of Cartes du Ciel-SkyChart only. You can download the last stable (still Beta) version from SourceForge. You also could try the latest development version from here.

Run the installer file skychart_3.xxxxx.exe, to install Cartes du Ciel-SkyChart in your prefered directory (i.e. C:\Program Files\Ciel)

At any time you can start the version 3 with skychart.exe, or the 2.76 version with ciel.exe