There is an image of clouds included as a resource in SpeechUXRes.dll of Windows Speech Recognition in Windows Vista Build 5212.0.winmain.050726-1915. It appears to be for the tutorial—a patent to which I do not have access at the moment, as well as a similar image in Windows Vista RTM, indicates such—but I could not start the tutorial. I have resized the image so that it can be used as a wallpaper.
(With that, Windows Vista Build 5112.winmain_beta1.050720-1600 is the first known build to include the Microsoft Speech Center).
Original version (1024x768).
Resized version (1920x1440).
Windows Vista Beta 2 5212 Speech Recognition Clouds
Windows Vista Beta 2 5212 Speech Recognition Clouds
"We do not view the desktop as a mode, legacy or otherwise."
Windows Vista: Microsoft Speech Center | Windows Vista Saved Search chronicle
Windows Vista: Microsoft Speech Center | Windows Vista Saved Search chronicle