GUI Button and a gameObject's position

Is there an easy way to have a GUI Button show up over a game object? I'm aiming for various items on a desk that have writing on them saying what will happen if the user clicks on them. (E.g. keys for "Shop", paper for "Write".) I was hoping this would be simpler than making the objects clickable and just positioning GUITextures over them.

You can ask the camera where any point in world space will be in screen space.

Try this to get a feeling (untested code, might contain errors):

public class Example : MonoBehavior
{
    // Bind target to the object it should follow.
    public Transform target;

    // We use update to obtain the position in this
    // example so we need to keep it until OnGUI.
    Vector3 point;

    void Update()
    {
        // Find screen position for target
        point = Camera.main.WorldToScreenPoint(target.position);
    }

    void OnGUI()
    {
        // In case point.y is inverted, just subtract it from the screen height.
        Rect rect = new Rect(point.x, point.y, 100, 50); 

        if (GUI.Button(rect, "Button")
        { 
            // Button clicked.
        }
    }
}

http://answers.unity3d.com/questions/5045/using-a-gui-button-to-stop-a-gameobject-movement

hi, i didnt understand where do i have to subtract the the point.y im nbot sure if im using scree height i have this:

 void Update()
{
    // Find screen position for target
    point = Camera.main.WorldToScreenPoint(target.position);
}


 void OnGUI()
 {
 float yPos = 5.0f;
 float xPos = 5.0f;
 float width = ( Screen.width >= 960 || Screen.height >= 960 ) ? 100 : 100;
 float height = ( Screen.width >= 960 || Screen.height >= 960 ) ? 100 : 100;
 float heightPlus = height + 0.0f;
 
 
 
 // In case point.y is inverted, just subtract it from the screen height.
    Rect rect = new Rect(point.x, point.y, 100, 100); 

****** I’ve tried change the screen height that appears in the code but, that is for some other static GUI buttons.

And one more question, how do put a position for example if want that the GUI button follow the object but in a specific position (a square object and the GUI button follow it but always in the corner)

appreciate the help!