We've shown you how to go about installing the new Windows 8 developer preview on a brand-new hard drive or a partition of your existing hard drive--that's easy.
However, most of you probably just want to check out Windows 8 without making a commitment to installing the OS on its own separate drive (or drive portion). No problem! You can still fiddle with the new OS in an environment that's much easier to remove once tinkering time ends, and that's all thanks to the power of virtual machines--applications which let you run a virtual PC inside your PC (cue Inception music).
See also: Microsoft Windows 8 review
Go grab VirtualBox and install the default package. Once you're finished, you'll open right into a fresh copy of the application. This is where you'll begin creating your system inside your system.
To start, click on the giant "New" button in the upper-left corner of the app. Give your virtual machine a clever name and select Window 7 as the operating system. Make sure that your choice of OS (32-bit or 64-bit) matches whichever version of Windows 8 you downloaded.
Click "Next" and you'll be taken to a screen that asks how much memory you'd like to devote to the virtual operating system. The 32-bit version of Windows 8 requires one gigabyte at minimum, and the 64-bit version requires two, but the more RAM you can give them, the better they'll run. Click "Next" once you've made your choice.
Leave the "Virtual Hard Disk" options and subsequent "Create New Virtual Disk" options exactly as they are, unless you think you'll need to access your virtual hard drive in a separate virtual machine application. You can select either a "Dynamically allocated" or "Fixed size" virtual hard drive based on your personal preferences -- we suggest you use the "Dynamically allocated" disk on our installation. On the next screen, make sure that your virtual disk has at least 16 gigabytes allocated to it for the 32-bit version of Windows 8. The 64-bit version needs a minimum of 20 gigabytes.
Once you're ready, click Next to create your virtual machine.
When your new virtual PC is ready, it will appear in VirtualBox's list of available machines (powered off at the moment, we note). Highlight it and click the big "Settings" button. If your system supports hardware virtualization, you can give your virtual machine access to additional CPU cores via the System submenu. If you don't know whether your CPU supports hardware virtualization, you can check for yourself on Intel and AMD's Web sites. For Intel processors, look up your own processor model and check for virtualization under "Advanced Features". For AMD processors, look up your processor model and look for a feature listing called "AMD Virtualization Technology".
Now click on the "Storage" submenu and click on the "Empty" line underneath your "IDE Controller." Click on the little CD icon next to the CD/DVD drive listing, and then select the option to "Choose a virtual CD/DVD disk file." Scroll for the Windows 8 .iso file you previously downloaded to your actual (not virtual) system and load that up. Now click on the big "OK" button at the bottom of the overall "Settings" window.
Cross your fingers and click on the big "Start" button to load your virtual machine for the first time. If all has gone well, the first thing you'll see is an annoying pop-up message that tells you about your keyboard and mouse capturing options. Ignore it. VirtualBox will boot and go right into the Windows 8 installation mechanism. Now take a breath: You've made it past the tricky part. And before you know it, you'll be fiddling around in Windows 8's funky new user interface faster than you can say, "Virtualwho?"
Now have fun in Windows 8!