Mask with action script question!

Anyone know how to get the mask to work with action script like in this site:

http://www.ziggystudio.com/v1/main.htm

Look at how the upper pictures load and unload?

How do I do that? I know action script has a way, but any direction as to find a similar tutorial?

Is it done with [font=Courier New]LoadMovie[/font]? to [font=Courier New]target[/font] or to [font=Courier New]level[/font]?

advice.