Welcome niners
Don't re-encode
You need only to re-encode your audio from 44.1Khz to 48Khz.
So first, you have to demux each of your .DAT files to .m1v and .mp2, and re-encode the audio ONLY.
Then, all your MPEG-1 VCDs that are encoded at 29.97fps, mux them with your new audio, and you're done!
The VCDs that are 23.976, run the program "pulldown.exe" against them, and then mux them with your new encoded audio. That should be all you need to do
Now you can use TMPGEnc DVD Author to import them and create your DVD.
Edit: I should have read your post better
You want 12 episodes on each DVD So you will have to re-encode your video. Keep in mind that you will loose quality by re-encoding from MPEG-1 again to MPEG-1
-kwag