Follow mouse issue

I am using the following code to have a piece of text follow the mouse…
onClipEvent (load) {
_x = 0;
_y = 0;
speed = 6;
}
onClipEvent (enterFrame) {
endX = _root._xmouse;
endY = _root._ymouse;
_x += (endX-_x)/speed;
_y += (endY-_y)/speed;
}

I want it to do this only when it is over a designated area. So, if you hover near the piece of text, it will follow the mouse, but if you roll off that designated area, it will ease back to it’s original state.
How could I do this? The way it currently is, is that it just follows the mouse whereever it is on the screen.
Thanks very much.