But if you have a Windows 8 Installations DVD and not a product key, you can use the Windows 8.1 / 8 with the following
product-keys to install it, but you can not activate Windows-8 with this keys! Only for Installation!

Language   Download Link   Windows 8.1 x64 or x32(x86) English 64-bit (x64)    Download (3.8 GB)     Windows-8.1 64 / x64 Bit Download English 32-bit (x86)    Download (2.8 GB)    Windows-8.1 32 / x86 Bit Download English (United Kingdom) 64-bit (x64)    Download (3.8 GB)     Windows-8.1 64 / x64 Bit Download English (United Kingdom) 32-bit (x86)    Download (2.8 GB)    Windows-8.1 32 / x86 Bit Download       Arabic 64-bit (x64)    Download (2.8 GB)       Windows-8.1 64 / x64 Bit Download Arabic 32-bit (x86)    Download (3.8 GB)     Windows-8.1 32 / x86 Bit Download Chinese (Simplified) 64-bit (x64)    Download (3.9 GB)      Windows-8.1 64 / x64 Bit Download Chinese (Simplified) 32-bit (x86)    Download (2.9 GB)      Windows-8.1 32 / x86 Bit Download Chinese (Traditional) 64-bit (x64)    Download (3.9 GB)       Windows-8.1 64 / x64 Bit Download Chinese (Traditional) 32-bit (x86)    Download (2.9 GB)    Windows-8.1 32 / x86 Bit Download French 64-bit (x64)    Download (3.8 GB)       Windows-8.1 64 / x64 Bit Download French 32-bit (x86)    Download (2.8 GB)     Windows-8.1 32 / x86 Bit Download German 64-bit (x64)    Download (3.8 GB)       Windows-8.1 64 / x64 Bit Download German 32-bit (x86)    Download (2.8 GB)    Windows-8.1 32 / x86 Bit Download Japanese 64-bit (x64)    Download (3.8 GB)       Windows-8.1 64 / x64 Bit Download Japanese 32-bit (x86)    Download (2.8 GB)      Windows-8.1 32 / x86 Bit Download Korean 64-bit (x64)    Download (3.8 GB)      Windows-8.1 64 / x64 Bit Download Korean 32-bit (x86)    Download (2.8 GB)      Windows-8.1 32 / x86 Bit Download Portuguese (Brazil) 64-bit (x64)    Download (3.7 GB)       Windows-8.1 64 / x64 Bit Download Portuguese (Brazil) 32-bit (x86)    Download (2.8 GB)      Windows-8.1 32 / x86 Bit Download Russian 64-bit (x64)    Download (3.7 GB)     Windows-8.1 64 / x64 Bit Download Russian 32-bit (x86)    Download (2.8 GB)   Windows-8.1 32 / x86 Bit Download Spanish 64-bit (x64)    Download (3.8 GB)      Windows-8.1 64 / x64 Bit Download Spanish 32-bit (x86)    Download (2.8 GB)      Windows-8.1 32 / x86 Bit Download Swedish 64-bit (x64)    Download (3.7 GB)       Windows-8.1 64 / x64 Bit Download Swedish 32-bit (x86)    Download (2.7 GB)      Windows-8.1 32 / x86 Bit Download Turkish 64-bit (x64)    Download (3.7 GB)      Windows-8.1 64 / x64 Bit Download Turkish 32-bit (x86)    Download (2.7 GB)    Windows-8.1 32 / x86 Bit Download

Windows RT 8.1 Preview requires that you have a PC already running Windows RT with 10 GB of free storage space.

Source