I've used Windows speech to text in WinXP Tablet PC edition. I believe it's pretty much the same as the one in Vista. Had to train it some, but it was still getting a lot of stuff wrong. With the built in microphone on my laptopt, it was pretty hopeless, but with a better microphone it was passable. Though, I'm a fast typist and can probably type quite a bit faster than it would take me to speak the text and correct all the errors afterwards.
