Film-making is a big endeavor even when the film isn’t. Be it 3D, 2D, or Video, or whatever the best shorts have scripts, and smart film-makers write script in proper script formats. Writing scripts in Microsoft Word just doesn’t work. You need Celtx (I pronounce it “selt-ecks”); it’s free, and it runs on windows mac and linux.
Pre-production involves a lot more than just a script. You’re keeping track of how many characters you have, what actors will play them, what setting they need to be on and at what time of day they need to be there, whos lines are whos, how much your props will cost you, and so on and so on. Celtx does a many of things for you in a “fill it in as you go” sort of fashion. Then, the more meta-data you fill in, the more accurate your statistics will be.
The neatest feature of all is that you can bind your script to an online account so that new versions will be automatically uploaded. You can also register more than one person to a project, like for example, your whole crew! A web page can be automagically generated with a shot calendar, mini-forum, and shared editing not unlike google documents. It’s neat. It got me through a couple films where sunlight would have been an issue otherwise.