Are the AVIs uncompressed completely or are they using a codec?

If you use the DV AVI codec I believe the files will be quite large - it works out something like 1 minute is anywhere up to 100 meg

Someone correct me if this is wrong as I'm going off the top of my head here.

Check your codec and try and use the Cinepak codec for AVI if you can.

If you have then I'm at a loss too.