window.onload = rolloverInit;

function rolloverInit() {
     for (var i=0; i<document.images.length; i++) {
     if(document.images[i].parentNode.tagName == "A") {
          setupRollover(document.images[i]);
          }
     }
}

function setupRollover(thisImage) {
     thisImage.outImage = new Image();
     thisImage.outImage.src = thisImage.src;
     thisImage.onmouseout = rollOut;
     
     thisImage.clickImage = new Image();
     thisImage.clickImage.src = "images/" + thisImage.id + "-over.jpg";
     thisImage.onclick = rollClick;
     
     thisImage.overImage = new Image();
     thisImage.overImage.src = "images/" + thisImage.id + "-over.jpg";
     thisImage.onmouseover = rollOver;
}

function rollOver() {
     this.src = this.overImage.src;
}

function rollOut() {
     this.src = this.outImage.src;
}

function rollClick() {
     this.src = this.clickImage.src;
}