Just some interesting information, I found a company called akond that supplies ID capture software that makes use of some kind of altered CHDK software to control an array of Cannon cameras. The software fully supports the SX170IS (ver 101 and 100). I tried the software and it works. It allows the following functionality via USB:
* Live view (updates every 40ms or so)
* Image capture, view and download
* Other camera settings like white balance.
I've attached two files as proof.