Two suggestions:
1. Consider installing an older version of MacOS X in a virtual machine (one of the commercial ones), along with DVD Studio Pro and DVDEdit (or Encore). Make your video and audio assets (and graphics) in your current setup, then move them to the VM and build your DVD.
2. Create your assets and then have the manufacturer of the DVDs put together the disc itself. All responsibility for QA, etc., will rest with them.
I'm not sure, myself, if the hassle is worth it to try to deal with older applications. Why not oversee things and let the fabricator do the "dirty work"?
Good luck!