DVD re-authoring help

[keytohwy]

I've got a few DVDs that were made on a stand alone DVD burner.  Is there a way I can change the:

1)  Main menu screen

2)  Chapter markers

I'd prefer tools available on Mac OS X, but can revert to XP is needed.

Thanks!

[stantheman1976]

TMPGEnc DVD Author is a good user friendly program.  It does not re-encode either.