For those interested in getting Windows 8 Pro as early as possible, Microsoft is starting downloads of the operating system tonight at 12:01 am, presumably in all time zones, though I haven't found confirmation of that.
Prices for the various versions of the operating system have been known for some time now, but I'll mention two of the least expensive here. The upgrade from XP, Vista or Win 7 will cost $39.99 for a direct download. You can find the link to the upgrade here at Microsoft's site. You'll need to run the Upgrade Assistant to determine if your computer meets the requirements of this upgrade. The Upgrade Assistant can be downloaded and run without necessarily buying the system.
The least expensive path to Windows 8 comes to those who have recently purchased a computer with Windows 7 already installed. This type of upgrade will cost only $14.99, but will take more time to process. You can find the links for your particular country at this page.
For those worried about reinstalling, Windows 8 will allow you to completely wipe the hard drive once it has found the appropriate installation of an earlier Windows operating system. So a "clean" install is possible. If you have Windows 7 installed now, this might not be necessary. Take a look at this article at Ars Technica on the process of installing over Win 7.
