works 100% tested
http://www.saschahlusiak.de/downloads/gifwcx.zip
source:
http://www.saschahlusiak.de/downloads/gifwcx_source.zip
GIFWCX (v1.1):
This plugin provides you with the ability to
view into animated gif images and extract single frames.
"pack" a few single images (*.gif, *.bmp, *.png, *.jpg) to a single animated gif image.
append images to existing gif images.
delete frames of existing animated gif images.