How do you write a project brief?

I have been asked to write a project brief and the company have told me they want an interactive cd.
1 – How do i write a project brief?
2 – Initial requirements specification
3 – Initial design documentation

I am really desperate to know how to do this. Please feel free to e-mail personally or if someone could e-mail me with a set of the above or a link on how to that would be great