Windows 8 Consumer Preview ISO files (.iso) are provided as an alternative to using Windows 8 Consumer Preview Setup. If you are on a PC running Windows and want to install the consumer preview on another partition, another PC, or a virtual machine, we recommend you download Windows 8 Consumer Preview Setup and use the built-in tools for converting an ISO image into installation media, such as a DVD or USB bootable flash drive.
Windows 8 Consumer Preview is prerelease software that may be substantially modified before it’s commercially released. Microsoft makes no warranties, express or implied, with respect to the information provided here. Some product features and functionality may require additional hardware or software. 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.
Do you want to try Windows 8 already? Microsoft released a Developer Preview of the next version of Windows. I will recommend to install this system on a new partition on better in a virtual machine. Virtual Box is free virtual machine and support Windows 8.
First step, Download the appropriate Windows 8 ISO from the Microsoft Developer Network site, burn it to a DVD if you want to install on a test computer or in a new partition.
Install on a New Partition
To create a new partition on Windows Vista or 7, you have to open Control Panel and then Administrative Tools. Double-click on the Computer Management option. When that window appears, look for the "Disk Management" submenu under "Storage" on the left-hand sidebar.
Microsoft has updated the page dedicated to Windows 7 by announcing the availability to download the Release Candidate of Windows 7. If you are member of the MSDN and Technet , you can download RC1 immediately otherwise wait May 5 to be public.
Remember that the final version should arrive by the end of 2009 or starting 2010.