30-Day Vista Evaluation
It looks like Microsoft is offering you a 30-day evaluation of Vista on a pre-configured virtual hard drive. The download size is between 159mb and 1559mb, depending on the components downloaded.
For organizations with complex desktop infrastructures, whether large or small, Windows Vista Enterprise is the operating system designed specifically to help realize a better return on IT investments. In this VHD, you’ll have the opportunity to road-test new and improved features including management (e.g. MUI, BDD, etc…) usability (e.g. Search, Navigation, etc…) and security (UAC, Windows Defender, etc…), enhancements to the Windows Vista platform.