How to (batch-)convert Nokia E70 video clips (MP4) to AVI?

I am using a Nokia E70 to record short movie clips.

I can *play* these MP4 clips on a Windows PC with Nokia's own Media
Player or VLC, but I cannot import them into a video editing software
(Windows Movie Maker or Magix Video Deluxe), as the format/codec is
not recognized.

The GSpot Codec Information app - which claims to know 270 codecs -
cannot read/identify the codec of the E70 files.

I tried to convert them using MP4Cam2AVI, but for whatever reason,
these converted AVIs cannot be imported into Video Deluxe, either, and
their playback stutters (i.e., every second, there is a short "hiccup"
where the video seems to jump back a few milliseconds). Files from
other cameras and phones work fine.

What is - in your professional opinion :) - the best way to convert a
(huge) pile of these MP4 files to AVI or MPEG?

I am willing to install codecs and spend (some) money, but if I do it,
I would like to get good results - i.e., the less-than-stellar video
quality shouldn't be reduced during conversion.

Thanks.