y=0;
ad=new Array(y);
var bnum=new Number(Math.floor(99999999 * Math.random())+1);

//ad[y++]='<a href="http://www.alempleo.com/adserver/adserver-alfa.cgi?' + bnum + '+S=URL" target="_blank" onMouseOver="window.status=\'<<< Click Aqui ! >>>\'; return true" onMouseout="window.status=\'\';return true;"><img border="0" src="http://www.alempleo.com/adserver/adserver-alfa.cgi?' + bnum + '+S=IMG" alt="Haga Click Aqui !" width="468" height="60"></a>'
ad[y++]='<script language="javascript" src="http://www.astrolabio.net/javaserver/468x60-general.js"></script>'

x = Math.floor(Math.random()*(y));
document.write(ad[x]);