jmp = new Array();
img = new Array();
jmp[0] = "http://www1.sphere.ne.jp/nikkeiba/";
jmp[1] = "http://www.olympic-club.org/campaign5th/index.html";

img[0] = "http://www.radionikkei.jp/archives/banner/1209240698.gif";
img[1] = "http://www.radionikkei.jp/archives/banner/1209240728.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>");