First off check you local codes and see if audio recording with out permition is allowed. In some states you can go to state prison for recording voices with out the persons consent. If in fact you found the baby sitter abusing the baby or stealing and theres audio you will be lucky if to court just shreads the tape and doest turn the lawsuit against you. This may also include audio monitoring. That's why newer cameras don't have audio and come with sign's that say "warning you are under CCTV". Just trying to help. I would check with the police department first then get back to us. I am not to sure about audio streaming with x10 on-line, but...
If you buy a normal webcam that has audio you can try a site called ustream.tv they have a password protect feature and the va11a will work with the ustram client (driver Wise).
Hope this helps.