Sorry, but I haven't tried to do any animations using Gimp.
I don't know what tutorials you have tried, but here's a list of some good Gimp tutorials.
You should be able to find something in these to help you out.
Tutorials - Beginner | Intermediate | Expert | Photo Editing | Web | Script Authoring - produced by the Gimp Team
pixel2life.com - 81 tutorials written by individuals for Gimp.
On the left is a list of the different catagoties covered; 3D Effects, Animation, Basics and Navigation, etc. .....
Also a great resource for other tutorials, besides Gimp.GUG - an assortment of tutorials produced by the Gimp User Group
Grokking the GIMP - a online, open source book, written by Carey Bunks, explaining the different functions of Gimp.
A pretty in depth book available for free, online.