y = 0; ad = new Array(y);

ad[y++] = '<a href="http://blog.bdinfo.net/tj/counter.asp?tid=50&gid=3F969D43A1DF3642BA0022BBF739A1AE&url=http://game.bdinfo.net/" target="_blank"><img src="http://game.bdinfo.net/mini.jpg" border="0"></a>'

//Continue if more required
x = Math.floor(Math.random()*(y));
document.write(ad[x]);