$(document).ready(function() {
    $('.rollover').hover(function() {
        var imgSrcOut = $(this).attr('src');
        var imgExt = imgSrcOut.substring(imgSrcOut.length - 4, imgSrcOut.length);
        var imgSrcOver = imgSrcOut.substring(0, imgSrcOut.length - 4) + "_over" + imgExt;
        $(this).attr('src', imgSrcOver);
        //alert(imgSrc + "_over" + imgExt);
    }, function() {
        var imgSrcOver = $(this).attr('src');
        var imgExt = imgSrcOver.substring(imgSrcOver.length - 4, imgSrcOver.length);
        var imgSrcOut = imgSrcOver.substring(0, imgSrcOver.length - 9) + imgExt;
        $(this).attr('src', imgSrcOut);
    });
});