If you are an individual upgrading an existing computer, your only option at the moment is Windows 8 Pro. The basic consumer version of Windows 8 will not be available for standalone purchase until February 2, 2013.
For now, Windows RT and the basic version of Windows 8 are only available pre-installed on new computers. The differences between Windows 8 and Windows 8 Pro are minor. The big decision you'll have to make when buying a new system is if you want a Windows 8 or Windows RT device.
Windows RT is a different version created for devices with ARM processers. These processers, typically found in phones and tablets, use less power, which means longer battery life. At the moment, Windows RT is only available pre-installed on Microsoft's new Surface tablet and a handful of other devices.
Windows RT and Windows 8 look the same, but there's one key difference: Windows RT will not run your old Windows applications, only applications available through the Windows Store. That means no downloading any third-party apps from the Internet. The Windows Store has 5,000 apps in stock, but that number should grow over time. This closed approach is similar to the iPad and iPhone, which can only run applications sold through Apple's App Store.
Finally, are you a large company planning on buying a large number of licenses? If yes, check out Windows 8 Enterprise.
Is Windows 8 difficult to learn?
Windows 8 presents a completely new approach to using a Windows computer, and as with anything radically new, it takes some getting used to. Do not upgrade unless you can spare some time to familiarize yourself with the layout and settings. The new look borrows heavily from the iOS and Android mobile operating systems, but isn't nearly as intuitive.
Before you get scared off, know that it's not that hard to figure out the new system. It just takes a bit of effort and time, like learning any new program would. Microsoft took a big leap and created something new. Getting acclimatized is just a natural part of the process.
Some stores selling the Windows 8 products are offering classes. Staples, for example, will have free personalized training on the new system, as well as help moving old data over to a new computer.
How much does it cost?
Microsoft is dropping the $200 price of Windows 8 Pro for its big debut. Existing WIndows 7, WIndows Vista and WIndows XP (with SP3) users can upgrade to Windows 8 Pro for $40 online. If you'd prefer a physical copy shipped to you in a nice box, the price goes up to $70. The deal is good through the end of January.