How-to: installing Windows 8 without product key
 

Installing Windows 8 is a bit different than installing the previous version of Windows. Windows 7 you could install without entering a product key, but when you install Windows 8 you are required to fill in a key right-away. For a normal installation that doesn't matter much. But if you only want to experiment with Windows 8 for testing purposes, or for any other reason only will have it installed on your computer for a brief period, then it's a different question.

http://uk.hardware.info/reviews/3490...ut-product-key