url = new Array();
img = new Array();
// url
url[0] = "http://px.a8.net/svt/ejp?a8mat=1NWJVJ+DQ5SVM+19NM+BXB8X";
url[1] = "http://px.a8.net/svt/ejp?a8mat=1NWN0H+5YCTU+1MC0+60WN5";
// img
img[0] = "http://www.racetrack.jp/imges/keiba_b.gif";
img[1] = "http://www.racetrack.jp/imges/umanavi.gif";
n = Math.floor(Math.random()*url.length);
document.write("<a href='"+url[n]+"' target='_blank'>");
document.write("<img src='"+img[n]+"' border='0'>");
document.write("</a>");