Black Background

I made a small animation. After I rendered it, I put it in a video editing program and the character looks just fine but behind him is all black and no matter what I do I can't get rid of it.
In my video editing program I have a still photo that I want to use as the background, but I can't get rid of the black so I can see the character in front of the still photo.
Any body know how I can get rid of the black?
Thanks !
Comments
You need to render as an image sequence, usign PNG or Tiff as the format, if you want to have an alpha channel.
Yep, I was rendering in movie avi.
Rendered in still png and all looks great.
Thanks for your help !