1. Your computer has an x64 processor but is currently running the 32-bit version of Windows. If you want to install the 64-bit version of Windows 8, download the 64-bit ISO.
  2. You want to install Windows 8 on your Mac (iMac or Macbook) using Boot Camp software.
  3. You want to install Windows 8 on multiple computers. In that case, you can download the ISO once, create a bootable DVD and boot the other systems using this newly created Windows 8 disk.
  4. You plan to run Windows 8 as a Virtual Machine inside your existing copy of Windows.
  5. You are running Windows XP.
The universal product key for Windows 8 is TK8TP-9JN6P-7X7WW-RFFTV-B7QPF.
Will my software programs run inside Windows 8?
Before grabbing the ISO image of Windows 8, quickly run this setup utility and it will show a list of all software programs and hardware drivers on your system that are compatible with Windows 8. Alternatively, you can visit this page to see a list of all known software and hardware devices that are found to be working with Windows 8.
How should I go about installing Windows 8?
You can have Windows 8 on your computer in three ways – you can install Windows 8 side-by-side (also known as dual-boot), as a virtual machine (so that it runs inside your existing Windows just like any other software) or you can have Windows 8 as your primary OS (there’s no going back from here).
If you just want to try out Windows 8  but without modifying any of your existing set-up, the safest bet is to use a Virtual Machine. If you have a vacant disk partition or don’t mind creating one (it’s easy), go for the dual-boot option. Else, if you have a spare computer, you can consider upgrading to Windows 8 overwriting the previous installation of Windows.
Also note that if you are upgrading from Windows 8 Consumer Preview to the new Windows 8 Release Preview, none of your installed programs, files and account settings will be preserved though everything would be moved to the windows.old folder.