Today Microsoft released Windows 8 Release preview to the public, earlier than expected. It is pretty much the last version before the Windows 8 RTM. In couple of minutes you will be able to download, install and experience it. I recommend you to start downloading the ISO before you do anything. As many people are downloading it may take sometimes to download.
You can download and install Windows 8 RP on your test computer or in Virtual box. Even thou this is a better version than the Windows Consumer Preview, I recommend you not to install this on your working computer.
Download: Windows 8 Release Preview
Windows 8 Release Preview works great on the same hardware that powers Windows 7:
Processor: 1 gigahertz (GHz) or faster
RAM: 1 gigabyte (GB) (32-bit) or 2 GB (64-bit)
Hard disk space: 16 GB (32-bit) or 20 GB (64-bit)
Graphics card: Microsoft DirectX 9 graphics device with WDDM driver
Some other useful links -
Windows 8 Release preview Frequently asked Questions.
Important warning from Microsoft: If you decide to go back to your previous operating system, you’ll need to reinstall it from the recovery or installation media that came with your PC, which is typically DVD media. If you don’t have recovery media, you might be able to create it from a recovery partition on your PC using software provided by your PC manufacturer. Check the support section of your PC manufacturer’s website for more information. After you install Windows 8, you won’t be able to use the recovery partition on your PC to go back to your previous version of Windows.