You don't need the AUDIO_TS folder, it's there for the DVD-Audio format, which no one uses. On commercial movie DVD's, it's empty anyway.
Before you burn the VIDEO_TS directory to disk, take the above poster's advice. You should first "burn" it to an ISO image, then copy that ISO image (as a data copy) to your dvd.
Many newer DVD's have forms of copy protection that populate the VIDEO_TS directory with junk files, which,for whatever reason, makes Toast gag. Creating and ISO image "container" for the VIDEO_TS directory pacifies the burning process and allows you make backups of your movies.
For creating the ISO image, I use Dragon Burn (you could probably do the same thing in disk utility or Toast, but I find Dragon Burn works better). I then transfer that ISO image to DVD with Toast.
Just to make sure this isn't all moot, what version of MTR are you using? If you're still on 2.66, then you'll need to upgrade to the latest version. 2.66 is known not to work with newer DVDs.