Oh, damn. I can't use pre-made screencaps to make animations. I have to be able to go frame-by-frame and take them myself. For me it's not so much a problem of knowing how to animate as it is how to make the icon a small enough file size to use on LJ. :/

I use Adobe ImageReady, which is a web-centric extension of Photoshop. I also have Macromedia Fireworks, but only because I took a Fireworks/Dreamweaver class. I like ImageReady better. I'm not sure of any free/open source programs that allow you to animate though, sorry.