Configuration testing can be very painful. There are almost an infinite number of combinations of possible hardware (CPU, RAM, disk, etc.), operating system (Windows XP SP2, SuSE Linux, etc.), and relevant software (IE6, IE7, Firefox 2.0, etc.) to deal with. Here at Microsoft we maintain lots of configuration labs which have all sorts of different physical configurations, but that is a very expensive proposition most organizations just can’t afford. One way to help ease (but not eliminate) the pain of configuration testing is to use Virtual PC 2007. With VPC 2007 you can set up virtual "guest" machines with just about any configuration you like, running on a real "host" machine. The image below shows I have created a virtual guest machine running the SuSE 9.0 Linux-based OS with the Konqueror Web browser on my real host machine which is running Windows Vista. Setting up virtual machines is quite easy. VPC 2007 is available as a free download. VPC 2007 is intended primarily for use on host machines which run desktop OSes such as Windows Vista and Windows XP, but also runs just fine on server OSes such as Windows Server 2003. You can create virtual host machines with most desktop OSes, even, as my screenshot shows, non-Microsoft OSes. Each virtual machine consists of a large .vhd (virtual hard drive) file plus a small .vmc (virtual machine configuration) file. This means you can create and then save as many virtual machines as necessary. After installing VPC 2007 on your host machine, you can click on the New button on the VPC mini control panel to launch a wizard to walk you through creating a new virtual machine. Then you insert a bootable OS of your choice into your host CD drive, the install will launch, and you install the guest OS as normal. Next you can add and configure software onto the guest. When you close the VPC control, all changes will be saved to your .vhd and .vmc files and can be used later. Using VPC 2007 is most suitable for basic manual functionality testing. Alternatives and complements to using VPC 2007 for configuration testing are creating multi-boot systems and using the more powerful Virtual Server 2005 product.