jQuery(document).ready( function() {
    jQuery(".thumbnail a").hover( function() {
        var changeSrc01 = jQuery(this).find("img").attr("src").replace(/thum_(.*?)/,"img_$1");
        var changeSrc02 = jQuery(this).find("img").attr("src").replace(/thum_monthly_(.*?)jpg/,"tab_$1gif");
        jQuery("#img_monthly").attr("src", changeSrc01);
        jQuery("#img_tab").attr("src", changeSrc02);
        return false;
    });
});