[Help wanted] Physically-based rigging script

I realize this will take some work, and I do not have enough knowledge to do this by myself yet, so I am asking for some help.
What I want to do is this: The thing with most animation is that it looks, well, not jerky, but not following physics. I realized that any movement we make is mostly just momentum, with forces added. So what I want to make is a script that instead of keyframing the positions of bones, instead keyframes the forces that they are applying. So if you put a person’s arm out straight in frame 1, it will swing down unless you add a force to the elbow and shoulder. I know this probably needs Bullet (although I could write a simple physics engine if that is too hard to work out, but it seems like re-inventing the wheel with Bullet already in there). It would need to run on every frame change (would this be done with script linking?), and continue to run with user input.
I know Python; I have done a lot of scripting for the Game Engine, but not very much inside Blender. Could anybody give me some pointers?

This is a very challenging and rewarding area of interest.

I’ve posted a lot of my work in this area to my website. Check out ‘progranimation’ and ‘ragdoll marionette’ specifically.

I’ve also seen some cool work on the subject here http://pyppet.blogspot.com/
and an implementation of his work.

Also there is BRIK ragdoll toolkit

And here’s a great paper on the subject

@ross_m - I can’t believe I’ve never heard of that library before. That’s amazing. I’ll have to see how difficult it would be to port to 2.5

Also - there was a physics branch that implemented bullet for rigid body physics in the animation system but I haven’t seen much from that lately.