function swapBackground(ss) {
        if(ss == '1')
        {
            parent.document.body.style.backgroundAttachment='fixed';
            parent.document.body.style.backgroundImage='url(http://www.windows7thailand.com/images/theme_bg_1024_768.jpg)';
        }
        else if(ss == '2')
        {
            parent.document.body.style.backgroundAttachment='fixed';
            parent.document.body.style.backgroundImage='url(http://www.windows7thailand.com/images/theme_bg_1280_1024.jpg)';
        }
        else if(ss == '3')
        {
            parent.document.body.style.backgroundAttachment='fixed';
            parent.document.body.style.backgroundImage='url(http://www.windows7thailand.com/images/theme_bg_1440_900.jpg)';
        }
        else if(ss == '4')
        {
            parent.document.body.style.backgroundAttachment='fixed';
            parent.document.body.style.backgroundImage='url(http://www.windows7thailand.com/images/theme_bg_1680_1050.jpg)';
        }
        else if(ss == '5')
        {
            parent.document.body.style.backgroundAttachment='fixed';
            parent.document.body.style.backgroundImage='url(http://www.windows7thailand.com/images/theme_bg_1280_800.jpg)';
        }
        else if(ss == '6')
        {
            parent.document.body.style.backgroundAttachment='fixed';
            parent.document.body.style.backgroundImage='url(http://www.windows7thailand.com/images/theme_bg_other.jpg)';
        }
    }

    function chkResWidth() {           
        var w = screen.width;
        var h = screen.height;
        // translate detected width and return index
        if (w == 1024 && h == 768) swapBackground('1');
        else if (w == 1280 && h == 1024) swapBackground('2');
        else if (w == 1440 && h == 900) swapBackground('3');
        else if (w == 1680 && h == 1050) swapBackground('4');
        else if (w == 1280 && h == 800) swapBackground('5');
        else swapBackground('6');
    }