var how_many_ads = 2;
var now = new Date();
var sec = now.getSeconds();
var num = sec % how_many_ads;
var ad_content=new Array(); 

//-->
ad_content[0] ='<IFRAME FRAMEBORDER=0 MARGINWIDTH=0 MARGINHEIGHT=0 SCROLLING=NO WIDTH=728 HEIGHT=90 SRC=\"http://optimizedby.rmxads.com/st?ad_type=iframe&ad_size=728x90&section=258537\"></IFRAME>'
ad_content[1] ='<iframe src="http://view.atdmt.com/6IF/iview/148930437/direct/01?click=" frameborder="0" scrolling="no" marginheight="0" marginwidth="0" topmargin="0" leftmargin="0" allowtransparency="true" width="728" height="90"> <script language="JavaScript" type="text/javascript"> document.write(\'<a  href="http://clk.atdmt.com/6IF/go/148930437/direct/01/" target="_blank"><img src="http://view.atdmt.com/6IF/view/148930437/direct/01/"/></a>\'); </script><noscript><a href="http://clk.atdmt.com/6IF/go/148930437/direct/01/" target="_blank"><img border="0" src="http://view.atdmt.com/6IF/view/148930437/direct/01/" /></a></noscript></iframe>'

document.write( ad_content[num]  )