Isn't Open Source the most amazing idea?
Here's some free storyboard software. I expect I shall be more likely to scribble messy notes on the back of envelopes and sellotape them to the wall, but for those who are more plugged in, it may be useful.
Meanwhile, I am searching for software that will onion skin for me. This means that if your camera is hooked up to a computer, a ghostly afterimage of the last shot remains on the screen - so that positioning the next shot is much easier. It makes for smoother animations. I haven't used it much for my own animations, being of the bootstrap and homemade type of animator, but I think it may be worth finding one for this film.