There have been a couple threads on this (it's how I learned), but I've got nothing better to do, so...
Isolate the clip you'd like to animate using Quicktime Pro (or whatever works best for you)
Export to image sequence
Open your favorite GIF editor (I use fireworks)
Import as animation
Crop, edit, whatever
Save as an animated GIF and you're done!
You'll want to keep a minimum of 8/100 second between frames or it looks slow in IE.