function preload(imgObj,imgSrc){
  if(document.images) {
    eval(imgObj+' = new Image()');
    eval(imgObj+'.src = "'+imgSrc+'"');
  }
}

preload('power_up','http://www.gmaccessorydealer.com/images/nav-powersearch_up.gif');
preload('power_over','http://www.gmaccessorydealer.com/images/nav-powersearch_over.gif');
preload('mgr_up','http://www.gmaccessorydealer.com/images/nav-mgr_up.gif');
preload('mgr_over','http://www.gmaccessorydealer.com/images/nav-mgr_over.gif');
preload('home_up','http://www.gmaccessorydealer.com/images/nav-home_up.gif');
preload('home_over','http://www.gmaccessorydealer.com/images/nav-home_over.gif');
preload('cart_up','http://www.gmaccessorydealer.com/images/nav-shoppingcart_up.gif');
preload('cart_over','http://www.gmaccessorydealer.com/images/nav-shoppingcart_over.gif');
preload('search_up','http://www.gmaccessorydealer.com/images/nav-searchbynumber_up.gif');
preload('search_over','http://www.gmaccessorydealer.com/images/nav-searchbynumber_over.gif');

preload('buick_up','http://www.gmaccessorydealer.com/images/nav-mfr-buick_up.gif');
preload('buick_over','http://www.gmaccessorydealer.com/images/nav-mfr-buick_over.gif');
preload('buick_oval','http://www.gmaccessorydealer.com/images/nav-mfroval-buick.jpg');
preload('cadillac_up','http://www.gmaccessorydealer.com/images/nav-mfr-cadillac_up.gif');
preload('cadillac_over','http://www.gmaccessorydealer.com/images/nav-mfr-cadillac_over.gif');
preload('cadillac_oval','http://www.gmaccessorydealer.com/images/nav-mfroval-cadillac.jpg');
preload('chevrolet_up','http://www.gmaccessorydealer.com/images/nav-mfr-chevrolet_up.gif');
preload('chevrolet_over','http://www.gmaccessorydealer.com/images/nav-mfr-chevrolet_over.gif');
preload('chevrolet_oval','http://www.gmaccessorydealer.com/images/nav-mfroval-chevrolet.jpg');
preload('gmc_up','http://www.gmaccessorydealer.com/images/nav-mfr-gmc_up.gif');
preload('gmc_over','http://www.gmaccessorydealer.com/images/nav-mfr-gmc_over.gif');
preload('gmc_oval','http://www.gmaccessorydealer.com/images/nav-mfroval-gmc.jpg');
preload('hummer_up','http://www.gmaccessorydealer.com/images/nav-mfr-hummer_up.gif');
preload('hummer_over','http://www.gmaccessorydealer.com/images/nav-mfr-hummer_over.gif');
preload('hummer_oval','http://www.gmaccessorydealer.com/images/nav-mfroval-hummer.jpg');
preload('pontiac_up','http://www.gmaccessorydealer.com/images/nav-mfr-pontiac_up.gif');
preload('pontiac_over','http://www.gmaccessorydealer.com/images/nav-mfr-pontiac_over.gif');
preload('pontiac_oval','http://www.gmaccessorydealer.com/images/nav-mfroval-pontiac.jpg');

function changeImage(layer,imgName,imgObj){
    if(document.layers && layer!=null) eval('document.'+layer+'.document.images["'+imgName+'"].src = '+imgObj+'.src');
    else document.images[imgName].src = eval(imgObj+".src");
}