$(function () {
    var preLoad = new Object();

    $('img.over,input.over').not("[src*='_on.']").each(function(){
        var imgSrc = this.src;
        var fType = imgSrc.substring(imgSrc.lastIndexOf('.'));
        var imgName = imgSrc.substr(0, imgSrc.lastIndexOf('.'));
        var imgOver = imgName + '_on' + fType;

        preLoad[this.src] = new Image();
        preLoad[this.src].src = imgOver;

        $(this).hover(
            function (){
                this.src = imgOver;
            },
            function (){
                this.src = imgSrc;
            }
        );
    });
});