function initRollOverImages() {
var image_cache = new Object();
$("img.swap").each(function(i) {
var imgsrc = this.src;
var dot = this.src.lastIndexOf('.');
var imgsrc_on = this.src.substr(0, dot) + '_on' + this.src.substr(dot, 4);
image_cache[this.src] = new Image();
image_cache[this.src].src = imgsrc_on;
$(this).hover(
function() { this.src = imgsrc_on; },
function() { this.src = imgsrc; });
});
}

$(document).ready(initRollOverImages);