After upgrading a Boot Camp Windows 7 installation to Windows 8 I found that the Boot Camp drivers needed to be updating to regain control of the function keys and built-in camera.
The Boot Camp software is available at Apple Boot Camp Support Website.
After the download I found the installer failed to run with the error “The installer encountered errors before Boot Camp could be configured“.
It turns of some programs interfere with the Boot Camp installer, especially ones relating to video drivers.
For me LogMeIn turned out to be responsible and after uninstalling that the installation went as expected, however some seem to have had problems with AirDisplay and other software too.