Navigation Problem

Hi, I’m hoping that someone is able to help me with my problem. I am creating a system for children to encourage mouse based navigation. The interface is based on a street map with a number of houses on it, and its up to the kids to move a car around the street map. There are 2 navigation methods that need to be made:

  1. The car needs to follow the mouse but it only move within a certain area i.e. the on the road and not over the houses or any other part of the interface that isn’t a road. The code I have is below, but I dont know how to edit it:

onClipEvent (load) {
_x = 0;
_y = 0;
speed = 15;
}
onClipEvent (enterFrame) {
endX = _root._xmouse;
endY = _root._ymouse;
_x += (endX-_x)/speed;
_y += (endY-_y)/speed;
}

  1. The car needs to move to the point where the mouse is clicked, but the area is restricted only to the roads. The code for this is below, but again, I dont know how to edit it so that the car will only move within the road area:

onClipEvent (load) {
_x = 0;
_y = 0;
speed = 15;
}
onClipEvent (mouseDown) {
endX = _root._xmouse;
endY = _root._ymouse;
}
onClipEvent (enterFrame) {
_x += (endX-_x)/speed;
_y += (endY-_y)/speed;
}

I hope that makes sense! I know it can be done, but I don’t how to do it, as I have just started using Flash.Can anyone help me please??? Thanks