function preload() {
 img1 = new Image();
 img1.src = "/images/menu01_over.gif";
 img2 = new Image();
 img2.src = "/images/menu02_over.gif";
 img3 = new Image();
 img3.src = "/images/menu03_over.gif";
 img4 = new Image();
 img4.src = "/images/menu04_over.gif";
 img5 = new Image();
 img5.src = "/images/menu05_over.gif";
}