Hi
First using an image editor remove the blue and red colour, save the image as PNG should show the transparency.
It may be best to create a background around the rings, this will help in hiding the video.
The ring image filling the frame with only the holes being transparent.
Using three overlay tracks you should be able to position the video behind the rings.
Resizing the videos.
Use Mask & Chroma Key to apply a Mask Frame which will effectively remove the corners, may help in poisoning the video.
The shape of the rings being the problem.
Similar effect here:-
http://www.youtube.com/watch?v=O9gfy75xIOw