How to install Windows 10 January Build (9926) on Oracle VirtualBox
Microsoft has just released the latest build of Windows 10. New features and changes include a more polished Start menu, Cortana on the desktop, new Settings, Photos, Maps and Xbox apps, and the ability to connect to wireless audio and video. As with the previous builds, this is a very early version of the OS, so you wouldn’t be advised to run it as your main operating system, and while you could set it to dual boot, running it in a virtualized environment is probably a more sensible idea.
To set up Windows 10 in VirtualBox, launch the software and click New in the Manager window. In the Create Virtual Machine dialog box enter "Windows 10" as the name of the operating system. Select Windows 8.1 as the version. (Choose Windows 8.1 (64bit) if you have a 64-bit ISO) Hit Next.
Set the Memory Size. The recommended figure should be fine. On the following screen choose to "Create a virtual hard drive now" and click Create. Accept VDI (VirtualBox Disk Image) as the hard drive file type. You’ll be asked if you want the new virtual hard drive to be dynamically altered (it will resize as required) or a fixed size. The latter option is faster, so select that.
Click Create and VirtualBox will begin building the drive.
When done, click the Start button in the Manager. In the "Select start-up disk" window, click the folder icon and navigate to the Windows 10 ISO.
Click Start and Windows 10 should begin to load. Select your language settings, then click the "Install now" button. Accept the license terms. Choose the "Custom: Install Windows only (advanced)" option.
Click Next, and the installation process will begin, rebooting as necessary.
When it’s done, you’ll be given the option of using express settings, or customizing things. It’s easiest to select the first one. Sign in with your Microsoft account (entering a code as required), and then finalize everything else.
Windows 10 will start and the first things you’ll see are your desktop and the taskbar with a "Search the web and Windows" search box. This is where you can also access Cortana, although "she's" not available if you live outside the US (she's certainly not available in the UK). Next to this is the button for Task View, then there's buttons for Internet Explorer (no Spartan in this build). File Explorer and the Windows Store Beta. Hit the Start button to view the improved Start menu. You can switch to full screen mode here.
If you want to resize the OS window, click View in VirtualBox and select Fullscreen or Scaled Mode.
The simplest way to shut down Windows 10 when you no longer need it is to click the X in top right corner of VirtualBox and select "Power off the machine".
If VirtualBox encounters errors and fails to install Windows 10, take a look at the troubleshooting suggestions here.