Diego,
What program are / were you using to try to control the NeoSpeech voices?
The UltraHal Text-to-Speech program does work but the slider adjustments are touchy (very small increments effect a change).
Mine showed numbers of 4, 9, 13, etc. and 13 was pretty fast.
Nextup.com has a program called Text Aloud that can also control the NeoSpeech voices.
There is no provision within Hal (that I know of) to change voice speed on the fly.
If you're using Windows XP, you can go to the Control Panel, select Speech, select Text to Speech and adjust the voice speed. After you test it, select APPLY and when you restart Hal, the voice will be at that selected speed.
Hope this helps a bit!