Do a search on Animstack here at Gimpchat.
Here is a link to gimp registry where you can download the latest.
http://registry.gimp.org/node/26501You'll need to learn where to put the .scm for windows. I don't work in windows a lot so I'm not best person to ask where to put this file but search this forum. There is loads of info here and plenty of very knowledgable people.
Check out the videos for AnimStack, these video are a good learning source and demo of program in action. He has a snow flake which he multiplies the graphic several times and has them fall from top of screen to bottom in random order. This may be for you, but in reverse? I'm sure it possible to just swap a number or value here or there to get it done.
Take care,
WW