var imgDefault = /^(.*)_off(\.(gif|jpg|png))$/;
var imgActive = /^(.*)_on(\.(gif|jpg|png))$/;
var imgOut = "_off";
var imgOver = "_on";
var imgFX = new Array(); 

function fx(obj){
     if(document.images){
          if(obj.src.match(imgDefault)){
               obj.src = obj.src.replace(imgDefault, "$1" + imgOver + "$2");
               }
          else if(obj.src.match(imgActive)){
               obj.src = obj.src.replace(imgActive, "$1" + imgOut + "$2");
               }
          }
     }
	 
function preFX(){
     if(document.images){
          for(var i = 0; i < document.images.length; i++){
               if(document.images[i].src.match(imgDefault)){
                    imgFX[i] = new Image();
                    imgFX[i].src = document.images[i].src.replace(imgDefault, "$1" + imgOver + "$2");
                    }
               }
          }
     }

window.onload = function() { preFX(); }