One of the nice things about Q10 and WriteMonkey (the subjects of the first post in this topic) is that they both allow you to set a bottom margin for text. I use this to set the "bottom of the page" halfway up the screen. I hate text falling off the bottom of the screen.
If none of that made sense, this full-screen grab from WriteMonkey might help:
The four dots around the text (if you can see them) mark the margins.
But this is just a poor man's version of what is called "typewriter scrolling" -- where you can set a fixed cursor position (say in the middle of the screen). The extra benefit of this compared to WriteMonkey is that you see any text below the cursor as well. The Mac-only editor Writeroom has typewriter scrolling. Does anyone know of any Windows text editors that have this feature?