Mark is right. I love this program. This is an awesome piece of freeware. Does tons for changing and converting audio (one downside: can't convert midi files to another form).
We have done several workshops where teachers create digital stories w/ narration, images, video, etc. and we do all of our voice-over recordings and editing in this; as opposed to a costly product like SoundForge or some other application where, while it can do the job, the learning curve is too great for short term use.
One of the coolest things is transforming voices: you can take an adult male voice, adjust the pitch and speed, and have it sound like it was recorded by a 5 year old girl. (Graham, insert your joke about my manliness here.

)
I have also used it for our Academic Olympiad competition where students have to identify a piece of music, but I play the track entirely backwards (amazingly enough the theme to The Simpson's TV show sounds the same forwards and backwards

). The kids love trying to figure these out. A little "thinking outside the box" (or the box is backward in this case). Takes a good ear and some serious concentration to listen to the patterns in the US National Anthem and play them backward in your mind.