the easiest way is, go to the drwindows subdirectory called Dialogs.
usually in C:\Program Files\DrWidows\Dialogs
there you will find tons of .cfg files.
each one is a plain text file describing a dialog.
just open them in a text editor like notepad, modify them and save them with a new filename ending in .cfg, and that's all you have to do.
you can test then from the drwindows options page.
