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

ad[y++] = '<a href="http://travel1.bdinfo.net" target="_blank"><img src="http://www.bdinfo.net/2007tu/ly070611.gif" width="468" height="60" border="0"></a>';

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