Static MovieClip() function?

I was looking at a video tutorial, and in order to reference a MovieClip, the instructor used:
var mc:MovieClip = MovieClip(e.currentTarget);

What is the difference between using that, and just using:
var mc:MovieClip = e.currentTarget;

Also, is there any way to easily duplicate a MovieClip? (or any class for that matter) There was a function somewhere back there, but that created a dynamic class. I want an exact replica of the class and all it’s properties without manually changing over each and every value.