I’m trying to make a generic widget which can be used to ‘counter scroll’ overflow content onmouseover/mouse move.

All fine and well, I’ve knocked this up here for you to see an example:
The problem comes when trying to add ‘easing’ to the counteraction/ repositioning. NOTE: I cannot use jQuery or any other toolkit here must be real/raw JS.
I’ve tried a couple of things all produce very scrappy results. Can anyone think of a lean mean easing out solution for this?
EDIT: Ideally something that is cross browser and low overhead.
I’m posting this for the benefits of anyone else with the same question/problem.
In the end, the best, simplest cross-browser solution without any jQuery nonsense was simply to run a javascript loop with a timer. here’s the fiddle:
http://jsfiddle.net/4YeX9/1/
the basis of the code came from a really helpful blog post here:
http://shiriru.blogspot.com/2007/09/javascript-animation-simple-easing.html
hope it helps someone out there.