CrossHair Automatically Tracking Object

Hi,I want to use the CrossHair locking the Object.like this ex.
https://www.dropbox.com/lightbox/home/Text
CrossHair is GUITexture.how can I use it to track the Object?
when I input Alt Key and active it.
Please everybody can help me. thx .

What i understand about your problem is that you want to find out that on which game object crosshair is targeting. for that you need to raycast from your mouse x,y position (or from center of your crosshair) into the 3D scene.
here is a similar post with example which can help you.