Three basic factors affect file size. One factor is frame rate. TV uses 29.97 frames per second. Film uses 24 fps. [These are the North American standards - NTSC] High quality computer animations are usually 30 fps (computers play 30 fps better than 29.97 fps). If you reduce the frame rate, you get smaller file sizes. Another factor is the actual dimensions of the movie. Full screen TV/video is 720 pixels wide by 486 pixels high. DV is 720 x 480. The caveat is that these are rectangular pixels (based on TV screens) not the square ones found on computer monitors. If your software won't work with rectangular pixels (Poser and Bryce don't) you need to render at 720 x 540 and then use a video program (like Premiere or After Effects) to resize the animation to the desired rectangular pixel dimensions. Obviously, the smaller the dimensions of the animation, the smaller the file size. The third factor is that animations can be saved using different compression schemes (or none at all). The compression you choose affects both file size and file quality. Both divX compression (found in many of today's .avi files) and QuickTime (MPEG 4 or Sorenson compression) create good quality images with very reduced file sizes. There is always a trade off between image quality and file size and the compression schemes use different algorithms so the actual image itself makes a difference in both the quality and file size reduction they are able to produce. Thus, to reduce your file sizes you need to consider your output. If you're creating something to be put to TV or video tape, you're going to have large file sizes (high frame rate, full screen dimensions, and as little compression as you can for quality). If you're just creating something for playback on a computer, you can reduce the frame rate (15 or 12 fps usually works good), reduce the dimensions (320 x 240 is common) and apply whatever compression you want. I often create at a larger size (I work full screen broadcast quality at times) and then I reduce the frame rate, the dimensions, and compress the animation when I've got it finalized. That way I can test various combinations and pick the quality/file size that best fits my purposes.

Before they made me they broke the mold!
http://home.roadrunner.com/~kflach/