I did some research on this a while ago, actually And yeah, there are some italian fan pages that display animated pictures
Answering your question. "Is posting animated .gif/.swf images on Facebook possible?" The answer is no.
There was a bug a few months ago on Facebook Photos, and that's how they got to post this. They just made a .GIF image, and changed the format to .JPEG/.JPG manually (Right click >> Change name). Then they uploaded them to Facebook, and since they were already converted, Facebook accepted them.
This bug got so known that people started to do upload these pictures, until Facebook fixed it (not so long ago). The only way to currently do something similar is creating a Facebook Application and doing magics with FBML... but that takes some serious coding and knowledge!