I recommend using a DivX codec to to crate your AVI videos. It has pretty good compression qualities. I also recommend that you render out all the frames of your Anim8or animations as either bitmap (.bmp) or JPEG (.jpg) images, then using something like VirtualDub to composite the images into a video. There are a few reasons for doing it this way:
1. Rendering individual images allows you to pick up where the computer last left off if it crashes for any reason.
2. You can go back and tweak one or more frames if you need to.
3. You post-process the frames with various image packages.
4. You can composite using different codecs and/or frame rates.
5. Etcetera, etcetera, etcetera...