I think the problem might be the double compression. (It's compressed when it comes out of Bryce, and then compressed again when you render it in poser.) If your computer can handle it, you might want to try full frames when you render in bryce, and then try it in poser. If you can't handle the full frames, try lowering the compression settings on the divx codec, or maybe brightening up the poser scene. When you import into poser, you're importing a background avi, right? You're not using the avi as a texture for a square? (poser 5 only)