You can download a free trial of animation shop, made by Jasc. It also comes with paint shop pro. It gives you a timeline and you can use it like movie maker or imovie. You can then export it as gif
I made mine with Gimp. Take a picture, run one of the filters in script-fu . You have to fit within the size limitations allowed by the site where you want to use the avatar. There are usually restrictions on the pixel x pixel dimensions and/or on the total file size.
