when I set a background avi video the video is not showed in the stage and it is not rendered in the output video (only the particles appear). I use an uncompressed avi video rendered with adobe premiere or an uncompressed avi video rendered with virtualdub.
If I use a background image the image is displayed in the stage but the particle appear all white.
You can try some of the suggestions in this tutorial for getting your video to play.
The tutorial is written for Vegas, but the settings may correspond with similar ones in Premiere, or you can try the frameserving method.
Not sure about your second problem. Does it happen with any emitter you try?