The position of the object on the screen in relation to the world coodinates depend on the position of the camerat and the distance of the object away from the camera.
Try hardcoding some object positions and see where they pop on the screen, then analyze the values you are setting via mouse listener using those objects as a point of reference. Then you will be able to pinpoint your problem.
Node: you need to call updateGeometricState() or updateWorldVectors() after setting the local translation.
depends on where is ur box attached? is it attached to the root node? if it is directly attched to the root node, then u r doing the right thing. if not the local coordinates for the box is not the same as the world coordinates u retrieved.