MS Works comes bundled free with most laptops that run Windows (in the US). MS Works is perfectly fine. You could use notepad, but I would advise against it. When I bought my new laptop, it had a home edition of MS Office 7 bundled as part of the promotion. If you're a Mac person, I'm sure they also bundle a word processor. [For the uber-techies out there, there is also OpenOffice. It is a FREE office suite that is extremely competitive featurewise with MS Office. It also has a screenplay template available. For those who don't want to buy MS Office, do check into OpenOffice which has a Word, Powerpoint, and Excel equivalents. I digress.] Regardless, my suggestion was to help save new writers some money.
I like CeltX, I use CeltX, but it can be overkill. It also can be rather obstinate. It has LOTS of COOL features for indie developers. It has features to separate out character and create a screen bible, to list out all the scenes for setting up shooting schedules, features for notating SFX, etc. However, it is not well documented for help. The use of tabs can lead to frustrating results. It doesn't have the finesse of the other commercial applications for importing other formats. It is good for what it does but has its own learning curve.
For new screenwriters starting out, I want to emphasize that you don't need to shell out tons of money on software. You can take advantage of the freebies on hand. And I emphasize, there are pre-existing word templates you can download that already have the tab formats set, so all you need to do is start writing.
The BBC has a special Word (and Mac) template for both the US and British screenplay formats that you can download for free. It is also rather sophisticated and mirrors CeltX providing formating for TV, Screen, Radio, Play, and Graphic novel all in one form.
Yes, I used a ribbon typewriter so I learned how to set tab stops.

But even now, I have made a blank Word document that has my title page, and the script pages with the tabs set. The reason I enjoy it is that I can slip my document onto a flash drive and go anywhere with it without worrying about having to tote my laptop. I'm not tied to a specific application. Besides as a text file, we're talking on 200-400 KB, not MB. So if I need to modify a script on the fly, I can do so easily. I believe we are in agreement. Too many people worry about 'industry standard'. My intent was to lay out a very basic idea of what that 'standard' means structurally.
If writers are going to shell out money, use it to register their finished works with the WGA, Library of Congress, or other registry site. As a screenplay writer, there are lots of avenues to spend money--contests, festivals, coverage services, etc. My purpose was to suggest how one can save money and use readily available resources. Final Draft, CeltX, and other products aren't necessary to get started.