As the furore over Vista's failings and the cries for Microsoft to continue to support XP has shown, it matters what operating system (OS) you run. Some people like to keep their options open, however, by maintaining multiple PCs - the average PC Advisor reader's household has at least three. Some of you even admit to giving houseroom to a Mac.

But it's not just a matter of wanting to enjoy a variety of computing experiences that may lead you to experiment with a different OS, it's what that OS can do, how it behaves and the software it can run.

Perhaps you've just upgraded to Vista and found that some of your older software is no longer supported. Or maybe you've discovered an exciting new software package, only to find that it runs under Linux.

These are just two instances where you might want to run more than one OS, but you needn't buy two machines or set up a dual-boot to achieve this. Virtualisation is a much easier approach and, over the following pages, we'll show you how to use it.

Such software creates a ‘virtual' machine - a software emulation of a real PC. A virtual machine behaves exactly like a physical one, and you can install any OS you like on it. The only catch is that it must run on a PC.

Running a guest OS that's identical to the host OS might not seem particularly useful, but this technique adds security for those who use the same machine for both business and pleasure. For example, a virus, failed installation or corruption on the guest OS can't interfere with the host OS.

In the workshops that follow, we'll be using two virtualisation packages. We'll use Microsoft Virtual PC to run a second OS for which you have the disc (an older version of Windows, for example), and VMware Player to run a pre-prepared virtual machine of a free OS such as Linux.

Create a virtual machine with Microsoft Virtual PC 2007

1. Install Microsoft Virtual PC 2007. Officially, the program is supported only by XP Pro and the Enterprise, Ultimate and Business versions of Vista. If you try installing it under XP or Vista Home you'll get a warning message. Don't panic: it'll still work. Click ok to continue.

Microsoft Virtual PC 2007 - Step 1

2. Launch the program and the main console and a New Virtual Machine Wizard will appear. Since, as yet, no virtual machines exist, creating a new one is the only option available. If you're running the Home version of XP or Vista, you'll once again be warned that your OS isn't supported - just click ok.

Microsoft Virtual PC 2007 - Step 2