imageName = new Image(height, width);
    imageName.src = "image_filename";

var reappear = new Image(100, 75);
reappear.src = "golden_cup.gif";
var fade = new Image(100, 75);
fade.src = "fade.gif";

<IMG NAME = "golden_cup" HEIGHT = 100 WIDTH = 75 BORDER = 0 SRC = "golden_cup.gif">

Apres quoi onMouseOver et onMouseOut sont utilises dans la balise HREF pour permuter les images:
    onMouseOver = "golden_cup.src = fade.src";
    onMouseOut = "golden_cup.src = reappear.src";