You just should have added that line
body div.background
{height:500px;background: url(../images/YOUR-PIC) repeat-x;}
it was not thought as a replacement for
.background
{position:absolute;width:100%;height:130px;background:url(../images/light4.png) 0 -384px repeat-x;}
That could have stayed unchanged in the css in this case.
I tested that locally and it worked without a problem ...