ok got ya,
well thats easy, after renderering (for instance 1 night) you can save the animation at that point. then copy the animationpart that has been rendered from the map (default is the Bryce map) to another map and rename it to the name it has and ad a 1 like "animation 1.av'" This is because otherwise the ready part you rendered last night will be overwritten. You can now close the application Bryce, and do with the computer what ever you want. When you want to continiou with your animation rendering, simply start Bryce, open you animationfile and continiou rendering. after this second night do as before. (Copy the animationmovie to the other map with name animation 2.avi) This is how i do it, as my renderes sometimes takes a few weeks. To combine the animation 1 en 2 i use VirtualDub, an little app freedownloadable and not so heavy as Premiere. and i save the uncompressed and compressed version.
Hope this is what you were searching for :)
Greets, Henny