Want to test out Windows 10 Technical Preview, but don't want to take a chance it'll kill your PC? Your best bet is to install it as a virtual machine using VirtualBox. It's easier to do than you might think. Here are step-by-step instructions about how to do it.
1. Install VirtualBox
VirtualBox runs on Windows machines, Macs, and Linux machines, so you'll be able to install Windows 10 in just about any platform. Get it from here, download it, and install it. No special instructions needed.
2. Get the Windows 10 Technical Preview ISO File
Head to this page to get it. When you go there, click "Get started," and follow the instructions and prompts until you finally get to the download page. Choose your language and whether you want to download the 32-bit or 64-bit version. I downloaded the 64-bit version, because I installed it on a 64-bit machine. Some people have reported problems with installing the 64-bit version with VirtualBox, but my installation went without a hitch. Write down where you downloaded the ISO file, because you'll need to know that later.
3. Start the installation
Run VirtualBox and click the New icon on the upper-left side of the machine. From the screen that appears, type Windows 10 in the name field. Then from the Version drop-down box, select Windows 8.1, and choose either the 32-bit or 64-bit version, depending on the ISO you downloaded.
4. Select the amount of RAM
Next you'll be prompted to select how much RAM you want to devote to your Windows 10 virtual machine. You'll be shown a recommended amount of RAM. You can change it if you want, but I've used VirtualBox for several years and have created many virtual machines, and I've found its recommendations to be on target. So unless you know what you're doing and have a very good reason to change it, accept the recommendation.
5. Create a Virtual Hard Drive
In order to install Windows 10, you'll have to create a virtual hard drive for installing it. So from the screen that appears after you've selected the amount of RAM, click "Create a virtual hard drive." Choose VDI (VirtualBox Disk Image) as the file type. For the type of drive, you'll have a choice between one that is a fixed size and one that dynamically allocates space, that is, it grows larger if the operating system needs it. Your best bet is to choose a fixed size. That offers better performance. Click "Create" after you've made your choices.
6. Select your ISO as the startup disk
After you create the virtual hard drive, you'll be sent back to the VirtualBox main screen. Click the Start button. You'll be asked to "Select start-up disk." Head to where you downloaded the Windows 10 ISO file, click "Start," and the installation begins.
7. Finish installing Windows 10
From here on in, it's just like any normal Windows installation, with the usual occasional reboots. The reboots happen inside VirtualBox, not on your machine itself. There's only one important choice you need to make --- select "Custom: Install Windows only (advanced)" when you're given a choice between that and a standard installation.
8. Turn on the Start Menu
After the installation, Windows 10 will run as a virtual machine. But there will appear to be one thing missing: You may not see the new Windows Start Menu, which is for many people the whole point of Windows 10. You'll have to tell Windows to use it. To do that, right-click the taskbar and select Properties -->Start Menu. Then click "Use the Start Menu instead of the Start screen." After you do that, you'll have to log out of Windows 10, and then back in again. But after that, you'll see the new Start Menu in all of its glory.