To clarify: In the render room, on the "Output" tab, half way down the properties list, under "File Format" is a set of buttons. (See screen capture) If "Current Frame" is checked you will get a still as your render. If "Movie" is checked you will get a animation. In your case, you must have "Movie" checked and your default is to .avi format for movies. The Poser file isn't importing as an .avi, your RENDERS are .avi's. If you look in the Assembly Room, you will see the list of Objects in your file, and they won't say .avi there. Hope this helps! :D