norm = new Image();
norm.src = "./img/but.gif";
over = new Image();
over.src = "./img/over.gif"; 

function myMouseOver(actImgName)
  {
    window.document.getElementById(actImgName).src = over.src;
  }

function myMouseOut(actImgName,active)
  {
    window.document.getElementById(actImgName).src = norm.src;
    window.document.getElementById(active).src = over.src;
  }