TO speed up the audio the simple thing is to press the Ctrl key and while holding that down grab the end of the audio and squeeze it into a smaller length to match the video that is sped up. This will some what produce the effect you looking for .. Not sure this will work too smoothly without cross fading several tracks to get the audio back to normal and then sped up again .. some one else may have done this and might have better idea..

If you have Sound Forge, use the Pitch Bend effect to "rubber band" the audio. It works very well. However, getting it to stay more or less in sync with the video is going to take a lot of experimentation and retries.

Well, you're not going to understand very much of what's being said unless the speed hovers in about the 50% or less zone. So I say: make the sound start to speed up (use xberks method), then cut out the portion in the middle and use already recorded effects of a tape speeding up and slowing down then do the opposite at the slowed down side, of having the real sound slow to pitch. Cross fade the real with the sound effects. You could even put the sound effects on its own track under your regular audio track and just use a volume envelope on each track to make one track fade out as the other track comes up. So your real sound starts to speed up, then it crossfades to a sound effect of a audio tape speeding up, then slowing down, the it crossfades back to the real sound slowing down to an understandable pitch.
That may be the easiest way to accomplish something hardly anybody will notice. Unless it's really important to hear these voices 3 octaves higher.
Here's a couple of freebies:
http://www.soundsnap.com/taxonomy/term/7140

Thanks all. I will give the sugestions a try. Beginning part is people walking into a room, middle part is them saying "hi" and last part is them walking out the room. Can be flexible on the intro and outro sounds.

As much as I have used video velocity envelopes before, this is the first time I have been interested in keeping the sound - usually I discard it.

Maybe an audio velocity evelope that tracks the video velocity evelope should be a V9 feature.

It can sort of work that way. If your Video and Audio are locked together, you can grab the end of the clip. Hover mouse over the very edge of the end of a video clip and you'll see a square Icon appear with an arrow pointing east and west through it. Push 'Ctrl' and hold it. A wavy line will appear under the Icon. When the wavy line appears, you can left click and drag the video section longer or shorter. This speeds down or up, both video and audio. I just don't know if you can reach 300% using this method. But re-renders will get you there if it can't be done all at once. You'll then have to get into the Audio properties (right click on audio track and choose properties) and make sure the 'Pitch change' is checked on 'Lock to stretch' and 'Method' window says 'Classic'. This will make the pitch change with the speed.
Place your splits in the right place, and I think you can do it this way. Experimentation will get you there.
EDIT: I've never used the velocity envelope to speed up a video, so I don't know if you can lock the audio with it, but it almost seems likely. Maybe just do the audio properties thing, above, first before trying to stretch or shrink the video.
EDIT2: I just tried it and the audio won't lock to the velocity envelope. If you use my method, at top of this post, you can do the middle section that way, you'll just have to wing it to get the right speed. It's the speeding up or down part that will be hard to match, but I think you can fake it, by just shrinking the audio part (may need to render a new wave to do it) I just can't figure out how to make it change at a various rate from slow to fast or vice versa. I would have to go up and down in increments which seems like a big hassle. You'd have to make a split in the audio track every 20 - 30 frames or so and condense it a little faster. Then do the opposite to slow it down on the other side. But the middle part, at a constant speed can be done with the wavy line thing, above.
3rd and Final EDIT: You could do the whole thing using the 'Ctrl', wavy line, drag method. Using splits in BOTH VIDEO AND AUDIO at the speed up and slow down points to increment your way faster or slower, and the middle part at a constant speed. The speed up and slow down parts will be a little time consuming but can be done fairly quick. The drag and shrink or stretch works pretty fast, if playing by ear. Just zoom in on the timeline a little if making splits every 'so many' frames and get a feel for how much stretch or shrink to use. You're only talking about a couple of seconds going from normal speed to full speed and vice versa, so your splits only need to be in those sections, probably spaced about every 1/2 second or so. Or every 5 frames if you really want it to sound like it has a velocity envelope. But this way, the video and audio should stay matched all the way.
I Lied...EDIT 4. Just in case I confused you, and I probably did, the middle part I'm talking about is not the middle part you're talking about. I'm talking about the section between "starting to speed up" and "starting to slow down". (the once you get to 300% velocity section).
Also, it's that '"starting to speed up/down" section that needs the splits for incremental speed changes.