Rollover
function rollover() {
var images = document.getElementsByTagName("img");
for (var i = 0; i < images.length; i++) {
images[i].onmouseover = function() {
this.src = this.id + "_over.png";
}
images[i].onmouseout = function() {
this.src = this.id + "_default.png";
}
}
}
window.onload = rollover;