Some time ago I went through the whole problem of getting animation to work from Assimp. I ended up getting it right and I explained how here but I didn't test it vigorously, it might help you though. You're probably not setting up your final transform correctly because Assimp isn't very clear whether it is storing a specific matrix absolutely or relatively to its parent.

I also suggest you use a very simple model as Buckeye suggested (I used a cuboid subdivided into 2 cubes, each cube having one bone, basically a very low poly arm).