button1 = new Image();
button1.src = "imagesg/b_nav_01_on.gif";

button2 = new Image();
button2.src = "imagesg/b_nav_02_on.gif";

button3 = new Image();
button3.src = "imagesg/b_nav_03_on.gif";

button4 = new Image();
button4.src = "imagesg/b_nav_04_on.gif";

button5 = new Image();
button5.src = "imagesg/b_nav_05_on.gif";

function topnav(img_name,img_src) {
document[img_name].src=img_src;
}