I did a clean install over a Win 8 installation which I did from Win 7 and it wiped the whole disk clean installed Windows 8 AND activated it without me doing a thing. Great to know.
I have promised my self this time though with Win 8 that I am going to schedule images each week to avoid having to go through the time of installing all the updates ever again. Where I am it takes forever to download updates with our slow bandwidth.
Got myself a copy of Macrium Reflect Free edition with a live boot disk and it works just great.