Looking for a complete answer to 'scratch-offs'

I have searched the web and searched the forums, but I am yet to find a complete and understandable tutorial on creating ‘scratch-off’ games … maybe I’m missing something or maybe I’m just dumb.

Could someone please take the few minutes to explain exactly how to create this effect in Flash MX? I want to be able to have 2 layers (one with the ‘prize’ and one with the ‘metal’). The user will ‘scratch’ (by clicking, holding, and dragging around) to reveal the prize.

I have already read through all related topics in the forums that I could find, but still no luck. Thanx in advance for taking it slow with a newbie to kirupa.
-chris