Have you seen animated icons in your tabs? This has been working for a while, with IE and FF and Co.

All you have to do is create an animated GIF file as your "favicon.ico", and it is better to name it .gif, by the way.

Because icons can now be pretty much any image format, not just .ico

And if you need some favicon for your site, check this one out: http://www.favicon.cc

Many of these are free!