beperron:
Ok, I got it working -- I think it was my power supply. That is, I have a 9v battery I was using to connect to the board to make it portable. When I plugged the board into my computer, the onboard LED was much brighter and it worked. Can I just attribute this problem to a low 9v battery?
Not so much low as much as low current capablities. If you try to draw too much current from one it's output voltage just sags no matter what the state of charge of the battery is. Build a pack out of 6 series connected AA alkaline cells and you will be much better off.
Lefty