Very simple question? hitTest()

1)I have a animated mc, and i want it to react only when a particular area of it has been hit. How to achieve this? (I have solved this one)

2)How do i check collision for a dynamically attached mc?? I also need to check, which parent mc, that mc is a instance of…

3)How do i change the depth of a mc?

4)i am generating movieclips with random speed, but sometimes, the speed becomes the same, and thus two clips overlap, how do i prevent this?