A simple usb controlled switch
It doesn't have to be that complicated.  Get an Arduino and 2 NPN transistors.  Connect it up like this:







simulate this circuit &ndash; Schematic created using CircuitLab

You can either write the Arduino program to work standalone, or to listen for commands sent over USB.  Either way, you set one of the GPIOs high to start autofocus, and the other high to snap the photo.  If you want to get fancy, google for "arduino intervalometer" and there are a bazillion projects to choose from.