Blur question?

I’m guessing im taking an overly simplistic attempt at dynamic blur. I want a black oval movieclip to blur based on the mouse position. I have searched the site and read the tutorials but i cant get what i want.

//defining var based on mouse location
onClipEvent(mouseMove) {
var xpos = _root._xmouse;
var ypos = _root._ymouse;
}
//using mouse location variable to change blur
var myBlur = new flash.filters.BlurFilter(xpos,ypos,5);
var myTempFilters:Array = circle_mc.filters;
myTempFilters.push(myBlur);
circle_mc.filters = myTempFilters;

can anyone point me to a easy tutorial or let me know where i am going wrong.

thanks!