myGifCnt = 8;
myGifTbl = new Array(
   "img/btn/01.jpg",
   "img/btn/02.jpg",
   "img/btn/03.jpg",
   "img/btn/04.jpg",
   "img/btn/05.jpg",
   "img/btn/06.jpg",
   "img/btn/07.jpg",
   "img/btn/08.jpg"
);
mySrcTbl = new Array( myGifCnt );
for (i=0; i<myGifCnt; i++){
  mySrcTbl[i] = new Image();
  mySrcTbl[i].src = myGifTbl[i];
}

function myChange( myBtnNo , myTblNo ){
  document.images["myBtn"+myBtnNo].src = mySrcTbl[myTblNo].src;
}