Here is my experience converting MNGs to AVIs. I downloaded various programs from all over the place, and made a batch file that went something like this:
1) Use ADVMNG to convert each MNG to a bunch of PNGs
2) Use ABC (Advanced Batch Converter) to convert the PNGs to BMPs
3) Use MP3DECODE to convert each MP3 to a WAV (assuming each MNG has an MP3)
4) Use BMP2AVI to make each AVI (and mux the audio with the AVI)
Unfortunately, I could never get the sound and video synchronized. Plus I never found a CODEC I was happy with (either the AVI was too big, or the quality was too poor).
So I gave up. I'm not saying it can't be done, but I'm starting to wonder if it is worth the effort.
Kook