Since it is an upgrade disk you may encounter some issues while trying to activate windows 8 when you perform a clean install.
During install the Setup will check if any of the partitions on any fixed drives (not removable drives like USB flash)contain a “Windows” folder. It will store the results in the registry key
1 means clean install, 0 means it qualifies for an upgrade.
You might want to turn that 1 into a 0 before trying to activate your windows 8 installation.
After the installation you can turn it back without any further problems.