Does anyone know a freeware / open-source program capable of converting an AVI or an AVI converted to a sequence of image files to an animated GIF?
I intend these for use in instant messenger clients as custom emoticons.

I only know of trialware for such purposes. And those are Total Video Converter and any graphics program capable of editing animated gifs like Fireworks, ImageReady, PSP or whatever.

ive done that before using virtualdub. it can export a sequence of bmp/tga files (File/Save Image Sequence) and then ive used paintshop to batch resize/crop the images and turn them into a .gif