PopUp Height based on mouse location

PopUp Height based on mouse location

This is the code I'm currently working with:

function centerPopup(){
   //request data for centering
   var windowWidth = 650;
   var windowHeight = document.documentElement.clientHeight;
   var popupHeight = $("#popupContact").height();
   var popupWidth = $("#popupContact").width();
   //centering
   $("#popupContact").css({
      "position": "absolute",
      "top": windowHeight/5-popupHeight,
      "left": windowWidth/2-popupWidth/2
   });
   //only need force for IE6
   
   $("#backgroundPopup").css({
      "height": windowHeight
   });
   
}


Instead of the pop-up appearing relative to the document height, I'd like it to appear relative to where the mouse has clicked. Any help would be GREATLY appreciated.