JACKET_P pics are the pictures that are displayed by some players when you press stop on the DVD. Most Sony players show them. Also if you have a DVD changer/jukebox they usually show a small picture for the DVD's that have them.
DVD Text is the text displayed on the LCD of a standalone player. It shows the title of the movie. Not all players support it.
It is a simple process to add them both. The jacket pictures don't take up much room and there would be room to add them. You simply put another folder on the DVD called JACKET_P with 3 specially formatted MPGs on it (along with the VIDEO_TS and AUDIO_TS files). For DVD text you use a freeware program called titlewriter.
If you like I can make the files and email them to someone (RiK?).