Infinite Scrollbar Advanced Problem

Hi all !
i have done this nice tutorial on infinite scrollbar wich is nice.
but i would like to customise it a little bit but i dont know the right way to do it.
here is my code.

on (rollOver)
{
xcenter=150;
speed=1/20;

}
on (rollOut)
{
speed= 0;

}
onClipEvent (enterFrame)
{
var distance=_root._xmouse-xcenter;
_x-=(distance*speed);
if (_x > 0) _x=-300;
if (_x < -300) _x=0;
}

it is all working nice, but i would like a little modification on the on (rollout) function.

i would like speed decrease slowly to 0 in relation to the actual speed.

for exemple if my mouse is at the full left corner (on the roll over) the scrollbar is going to go at the full speed, so if i leave the scrollbar and go outside (on rollout) i would like the speed decrease to 0 in relation to the last speed i was on.

omg my english suck lol. i hope u can understand what i mean. :smiley:

i think it is about speed control and ease control.

well thanks if someone can help !
it will be very appreciated !
cya.