I've written dozens and dozens of scripts for clients that have been used in Captivate and RoboDemo movies. I usually use a specific document when I create the scripts. A student asked how much I would charge per download if people wanted to buy the document on my site.
I do not believe the document has much value. Instead, it's the content that my client's pay for. So here's a link to a Word document that you can use for free. Mind you, it's not an actual script from any client (that wouldn't be kosher). Instead, feel free to use the document--it may help you on your way to script-writing success.