function preLoadImages() {
    if (document.images) {

        pic1= new Image(66,9); 
        pic1.src="images/nav-availability-hover.png";
        
        pic2= new Image(54,9); 
        pic2.src="images/nav-contact-hover";
        
        pic3= new Image(115,9); 
        pic3.src="images/nav-designcentre-hover.gif";
        
        pic4= new Image(138,9); 
        pic4.src="images/nav-localarea-hover.gif";
        
    }
}

window.onload = preLoadImages();