Windows 8 will be available on 26th October 2012. Read more
The most exciting news is that Windows 8 will be available as an update if you are running Windows XP, Windows Vista, or Windows 7 just for $39.99 (downloadable). And if you want, you can add Windows Media Center for free through the “add features” option within Windows 8 Pro after your upgrade.
A packaged DVD version of the upgrade to Windows 8 Pro will be available for $69.99 during this promotion.