ros_arduino_bridge fighting me every step of the way, Raspberry Pi, Hydro, Wheezy

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I've been trying to avoid asking what I'm hoping has an obvious answer, but after 30 hours of struggling with this, it's time to ask the experts.

I've installed ROS (Hydro) on an Raspberry PI. It seems to have gone as well as could be expected. I can start roscore, etc.

I've already modified the arduino firmware to do what I wanted (simple encoder, different h-bridge) and it seems to be working from the serial monitor.

However, when I try to launch ros_arduino_bridge, I get the following:

ERROR:  cannot launch node of type [ros_arduino_python/arduino_node.py]: can't locate node [arduino_node.py] in package [ros_arduino_python]

I'm a total ros and python newb, and linux is not far behind. I know enough to be dangerous.

ROS lives (I think) in the directory ~/ros_catkin_ws.

Google isn't helping. I've been through fuerte from an image for the pi, groovy from an image, indigo from repository, and now hydro from repository.

Help?

Thanks,

Ed