I don't think this is exactly what you are looking for but here's what I did for a moving icon. I have only used it to make an animated PNG icon for an animated shortcut docklet with ObjectDock.
Create the icon in Realworld icon editor.
Open RealworldPaint.
For the size of the canvas, make it the same height as the icon and x times the length. (X being the number of frames you would like to be in the animation.
Copy/Past the icon into Realworld paint. Position it all the way on the left side of the canvas.
Make the next frame in Realworld icon editor.
Paste this into RealworldPaint and position it next to the first frame.
Repeat for all frames.
Save this as a .png image.
It can now be used as an animated PNG image for applications that support them.
I would assume that this also works for GIF animations as well, but have not tried it.
Hope this helped! =)