function rollOver(){
    var preLoad = new Object();
    $('#g-menu li img,#topbtn-blk img').not("[src*='_o.']").each(function(){
        var imgSrc = this.src;
        var fType = imgSrc.substring(imgSrc.lastIndexOf('.'));
        var imgName = imgSrc.substr(0, imgSrc.lastIndexOf('.'));
        var imgOver = imgName + '_o' + fType;
        preLoad[this.src] = new Image();
        preLoad[this.src].src = imgOver;
        $(this).hover(
            function (){
                this.src = imgOver;
            },
            function (){
                this.src = imgSrc;
            }
        );
    });
}

$(function(){
	rollOver();
});