browser = (((navigator.appName == "Netscape") && (parseInt(navigator.appVersion) >= 3 )) ||
          ((navigator.appName == "Microsoft Internet Explorer") && (parseInt(navigator.appVersion) >= 4 )));

if (browser) {
  if (document.images) {

    // nav normal image
    nrm01 = new Image();
    nrm01.src = "images/btn01nrm.jpg";
    nrm02 = new Image();
    nrm02.src = "images/btn02nrm.jpg";
    nrm03 = new Image();
    nrm03.src = "images/btn03nrm.jpg";
    nrm04 = new Image();
    nrm04.src = "images/btn04nrm.jpg";
    nrm05 = new Image();
    nrm05.src = "images/btn05nrm.jpg";

    // nav hover image
    hov01 = new Image();
    hov01.src = "images/btn01hov.jpg";
    hov02 = new Image();
    hov02.src = "images/btn02hov.jpg";
    hov03 = new Image();
    hov03.src = "images/btn03hov.jpg";
    hov04 = new Image();
    hov04.src = "images/btn04hov.jpg";
    hov05 = new Image();
    hov05.src = "images/btn05hov.jpg";
  }
}

function changeImage(imgObjId,imgObjName) {
  document.images[imgObjId].src = eval(imgObjName + ".src");
}