Hi Firestar,
It depends upon what you actually want to do. If you want a standalone video that will show the ambient background wherever you place it, then Terry is right: GIF is about the only—poor—choice.
If, however, you want to make videos with animation over a background that is part of the video, then various video editors offer “green screen†compositing of one track with a color designated as transparent over another track.
Pinnacle Studio offers this in some versions. Sony Vegas, which I use, is a better, more stable, choice. You can get into the business for less than $US 100. There may be less expensive programs to do it.
Regards,
Marty