How to add a new audio track to an existing movie ?

[thxtof]

Let me explain what I'm trying to do...

Doing a backup of Sleeping beauty, the widescreen version has english audio only, and the fullscreen version, on the same DVD, has in addition the Spanish and French audio track.

My question is what is the simplest way to create a backup with just the widescreen version, but add the Spanish and French audio from the other version?

Thanks :)
-Chris