i wanna change the intro for my dvd movies keeping the menu and everything

I WANNA ADD A FILE TO A BACKED UP DVD VIDEO...........WHAT I REALLY WANNA DO IS ADD A DIFFERENT INTRO TO MY DVD, SO WHEN SOMEONE PLAYS IT IN A REGULAR DVD PLAYER MY INTRO COME UP FIRST THEN THE DVD MOVIES STARTS AS USUAL..........I LEND DVD TO MY FRIENDS ALOT, SO I WANNA KNOW WHICH ONES ARE MINE....I WOULD LOVE TO KEEP THE ORIGINAL MOVIE WITH MENUS AND PREVIEWS AND EVRYTHING....JUS WITH DIFFERENT INTRO

It can be done with PGCEdit.
Author your intro clip first into it's own DVD so you have TWO DVD's...your main DVD and your intro clip DVD.
Open your main DVD in PGCEdit. Up at the top go Title->Import First Play (Startup) Clip, and follow the short instructions from there.

Simple