I'm going to post how to easly and freely(as in free beer) Overclock your audio books.
The software required is
wavosaur: an amazingly small executable audio editing program for windows, and
Audacity an amazing free audio editor that is open source and cross platform.
STEP 1
Open Wavosaur and open your audio project.
Click tools --) Silence remover --) Custom
Insert the level: -25.00
Insert the duration: 0.25
Press OK
Save the file as a WAV
Step 2
Open your WAV with Audacity.
Press CTRL + A or select the whole audio track manualy with your mouse.
Click Effect --) Change tempo
insert the Percent change:100 (you can make it slower or faster, as you like it yourself)
Press OK
File --) Export
Select the desired audio codec (mp3, ogg, ...)
If you have selected mp3, you should have a binary of lame downloaded to your pc and you have to know its location. In order to do that download it
here, extract the ZIP archive and put the file under "my documents" (or where you like it)
When exporting to mp3 Audacity wil prompt to ask for the "\lame_enc.dll" file. Just locate it on your pc and it will export to mp3
Have fun.