Planning to test Windows 7 but don’t fancy installing it. Microsoft have released a pre configured virtual hard disk (VHD) that can be used in a virtualization system such as Hyper V
The Microsoft VHD Test Drive Program provides customers with an enhanced server-based software evaluation experience that’s faster, better supported and more flexible. You can now access the entire catalog of pre-configured Microsoft and partner products and solutions in the VHD format and start evaluating and testing today from www.microsoft.com/vhd.
This download helps you evaluate the new features of Windows 7, Windows 7 has better ways to find and manage files—like Jump Lists and improved taskbar previews—to help you speed through everyday tasks. It's designed for faster and more reliable performance, so your PC just works the way you want it to. With 64-bit support, you can take full advantage of the latest powerful PCs. And great features like HomeGroup, Windows Media Center, and Windows Touch make new things possible. For more information about Windows 7, please go to http://www.microsoft.com/windows/windows-7/.
This is a preconfigured virtual machine set contained within the Virtual Hard Disk (VHD) format. Windows Server 2008 Hyper-V, Microsoft Hyper-V Server 2008, or the R2 versions of these products is required to use this virtual machine. Please refer to the system requirements section for more details.
More info about the Microsoft VHD Test Drive Program
You can download the VHD from here