>how to write a storyboard for any software?

I use Visio if I need to make a formal storyboard to distribute, normally I would do it informally on a big Artist Tablet or Whiteboard.

Also, I would typically do this only if the client requests, OR if during Use Case exercises two fairly different perspectives regarding what the software should do evolved and a decision is made. The sotyboard makes a nice approach for saying "are you absolutely sure this is what you want me to do before it costs you a lot of money"

HTH