var url_before = "/blogs/thon/images/banner_";
var url_after = ".jpg";
var min = 1;
var max = 24;
function showRndImg() {
   document.getElementById("banner").style.background = "url('" + (url_before + (min + Math.round(Math.random()*(max-min)) ) + url_after) + "');";
}

function writeRndImg(){
var bannerStyle = "background-image: url('" + (url_before + (min + Math.round(Math.random()*(max-min)) ) + url_after) + "');";
 document.write("<div id=\"banner\" style=\"" + bannerStyle + "\"");		 
 document.write("<div id=\"banner-inner\" class=\"pkg\" style=\"text-align:center;\">");
 document.write("<a href=\"/blogs/thon\"><img src=\"/blogs/thon/images/thon_kicker.png\" alt=\"Thon banner\" /></a></div></div>");
}