Microsoft has made Windows 8 Developer Preview available for download in either 32/86 bits or 64 bits. But so far only for the traditional X86 processors. But before you format your whole machine and sit back with Windows 8 on the screen its worth remembering that this is called a Developer Preview.
Developer Preview is particularly interesting, because in the package, Microsoft has placed development tools that let you program the apps to the new Metro-interface. But its only important if you are a developer. There is still a long way to go before we see the finished product. A good idea is to install Windows 8 on a separate hard drive or partition if you have important stuff on your PC.
After the download you can burn the image or the downloaded file to a dvd and boot from it to install the latest copy of Windows 8. For a step by step instructions on how to burn an image to a dvd click here.