jmp = new Array();
img = new Array();
jmp[0] = "http://school.radionikkei.jp/";
jmp[1] = "http://keiba.radionikkei.jp/keiba/contents/";

img[0] = "http://www.radionikkei.jp/archives/banner/1222242967.gif";
img[1] = "http://www.radionikkei.jp/archives/banner/1208511816.gif";

n = Math.floor(Math.random()*jmp.length);
document.write("<a href='"+jmp[n]+"'>");
document.write("<img src='"+img[n]+"' border='0'>");
document.write("</a>");