Whoa.. that site makes me dizzy.

My thoughts on your question:

Create a variable for the default speed of your scrolling. For instance:

var xVel = 1;

Create the scrolling movie clip. (assuming the clip will scroll on the main timeline and not within itself. (otherwise, this will all be done with a movie clip inside of another clip)

Create and place some buttons over top of the spots on your scrolling clip to catch the rollover and call the code.

The scrolling movie clip will be controlled by an onEnterFrame function that is looped.

Something like:

function onEnterFrame() {
var nextX = xVel + movieclip._x;
movieclip._x = nextX;
}

Have the rollover buttons trigger some code that will adjust the xVel variable. The further from 0 the variable the faster it move, the closer to 0 the slower it goes, and at 0 it will be stopped. If you go negative, it will be go in the opposite direction.

I hope this all makes sense. I'm trying to adopt this from a similar thing I did using object code tied to a movie clip in actionscript 2. Let me know if you need anymore help :)