You could enter separate start and end frame numbers for each part. Generally, though, I would recommend to use AVI only for short renders so you can immediately view the resulting movie. For final renders and longer movies I recommend to render to individual images and make a movie file out of these separately using a program such as VirtualDub. This lets you easily experiment with e.g. compression settings without having to re-render the entire animation in Ultra Fractal, and gives you more options such as MPG output.
You could enter separate start and end frame numbers for each part. Generally, though, I would recommend to use AVI only for short renders so you can immediately view the resulting movie. For final renders and longer movies I recommend to render to individual images and make a movie file out of these separately using a program such as VirtualDub. This lets you easily experiment with e.g. compression settings without having to re-render the entire animation in Ultra Fractal, and gives you more options such as MPG output.