Enjoy Windows Vista SP1 on your browser without out having to install anything

Microsoft Virtual lab is providing a free test-drive of Windows Vista Ultimate SP1, the latest operating system from Microsoft without having to install it on your PC. You needn’t install anything, just use your browser and enjoy all features of Vista.
The Windows Vista version hosted in the test drive contains most of the functionality of the regular versions, but browsing the internet is not enabled. The test drive requires Internet Explorer 6 or later, a browser plug-in, and a broadband Internet connection.
A minimum 1024 x 768 screen resolution is recommended. (via – vishal)
Windows Vista Test drive