If you haven't heard of it take a look at www.celtx.com for a very useful program for script writing including story boarding and even scheduling. A free download with video tutorials and detailed help at http//wiki.celtx.com available in multiple languages and for Windows, Mac X and Linux OS. I have tried it and it works.
This is a really useful and bug free (in my experience) piece of software, been using it for a couple of years and in that time it has grown into an indispensible tool. Why buy something like Final draft when you can get this for free (at the moment).