var preimg = new Array(9);

for (i=1;i<10;i++){
  preimg[i] = new Image;
  preimg[i].src = pass + "img/menu"+(i)+"_ro.gif";
}

function chimg(over){
img1 = new Image;
img1.src = pass +"img/"+over+"_ro.gif";
document.images[over].src = img1.src;
return true;
}

function bkimg(out){
img2 = new Image;
img2.src = pass +"img/"+out+".gif";
document.images[out].src = img2.src;
return true;
}