Make the file in Notepad (or your favorite text editor)
Save it as a .txt
Make sure Windows is set to show file extensions
Rename the file, and make it like MyError.cfg (instead of MyError.txt)
Put it in the Dr. Windows error folder
Test it with Dr. Windows
(Edit: I used to be a huge fan of Dr. Windows, so if you need help making the errors just post again here or PM me
)