Windows 8 License clearly requires a qualifying operating System be installed and that Windows 8 be Installed over the top of the Qualifying Operating system. Can be installed other ways but will not activate. An clean install can be performed from within the Windows 8 Install by clicking save nothing when asked. This will wipe the drive, format and install.. The only way around this is to By the System Builder or OEM copy of Windows 8 from an online store such as New Egg or Amazon. List for around $125.00 US. There have been several sales with prices around $85.00 US. Remember OEM version comes with no support.
With previous versions of Windows you could use an Upgrade copy of Windows to do a complete clean install by inserting the License of the Windows you were upgrading from.
Can you do a clean install of Windows 8 to a separate partition by simply giving the License Key of Windows Vista without installing over Vista.