Microsoft has released a public beta of desktop virtualization software to run legacy Windows applications on Windows Vista.
Microsoft Enterprise Desktop Virtualization (MED-V) allows computers running Vista also run Windows XP or Windows 2000. Virtualization becomes a strategic issue for the conquest of new users of Vista in the business world.
The beta can be downloaded here. A short survey will need to be answered before downloading the software.
You can read more at Microsoft Enterprise Desktop Virtualization for Vista