I'm putting together instructions for our users to test their microphones. Vista and 7 changed the Sound Recorder so it doesn't play back sound. Hence it's not good for testing sound (they have to save the file, find it, open it, inevitably get the Windows Media Player "first time" experience... at which time they've forgotten what they were doing).
The only other option I see for testing the Microphone is to click Start> Control Panel> Sound> Microphone > Configure> Set up Microphone (and hope that they don't have their Control panel in Classic setup.
I know there are ways to launch the Sound dialog via the command line like this.