I'm urgently trying to figure out how to do a certain style of animation in Flash MX. I want to have the effect of a line being "drawn", as if by an invisible pencil. How can this be done?

I wondered if this might be done somehow with a Motion Tween, but it didn't seem to work. Is there perhaps a 'mouse capture' tool that allows Flash to capture the movement of the mouse and the lines or shapes it makes on the screen?

I've seen it on websites such as Pencilmation.com, and need to know how to do it for a school assignment.

All help is much appreciated. If you know how to do this, please help. I'm desperate.

Thankyou!