Imagevue does not stretch background images. The best way is to make sure your background image(or swf) is "big enough". Another strategy is to make sure your image fades into the background color so there is a smooth transition.
If you are serious about getting your SWF/image to stretch to the screen, it can be done with some code in Flash. Please do not try this if you are not familiar with flash:
#Create a new Flash, make your background or import your image. Make sure to convert your image/background into a movieClip. Give the movieclip an instancename "background" and add the following code to the frame:
mybackground = new Object();
mybackground.onResize = function(){
background._width = Stage.width;
background._height = stage.height;
}
Stage.addListener(mybackground);
Export for Flash 7, AS2