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] ='<button style="width:728;height:90;background:transparent;border:0;padding:0;cursor:hand" onclick="window.location.href=\'http://www.backchina.com/ads/adclick.php?bannerid=102&zoneid=46\'"><object classid="clsid:D27CDB6E-AE6D-11cf-96B8-444553540000" codebase="http://download.macromedia.com/pub/shockwave/cabs/flash/swflash.cab#version=6,0,29,0" width="728" height="90">  <param name="movie" value="/ads/banners/forex_728x90.swf">  <param name="quality" value="high"> <param name="Wmode" value="Opaque"> <embed src="/ads/banners/forex_728x90.swf" quality="high" pluginspage="http://www.macromedia.com/go/getflashplayer" type="application/x-shockwave-flash" width="728" height="90"></embed></object></button>'
ad_content[1] ='<A HREF=http://yp.backchina.com/ target=_blank><img src=http://www.backchina.org/ads/banners/chineseRestaurant_728x90.jpg WIDTH=728 HEIGHT=90 BORDER=0></A>'
document.write( ad_content[num]  )