How to Leave Blurry Trail Behind Ship/Character?

i was reading another thread about bitmapdata, and i saw something like this:
http://img170.imageshack.us/my.php?image=vectorwarszh4.swf

i thought it was very cool how when everything moves in the game it leaves a blurry trail behind. But, i am unsure how to do this. obviously with bitmapdata, and filters… i’m not exactly sure what to do.

lets say i start with a movieclip from my library


var box:Box = new Box();
var filter:BlurFilter = new BlurFilter(6,6);
box.filters = [filter];
//...then what?

i’m not even sure if that’s right… what do i do?