var rand3 = Math.random();
var rn3 = Math.floor(rand3*100+1);

<!-- Ferrepress.com (Imcoinsa) 1229 visitas a día 13/06/2007
if(rn3>=0 && rn3<33) 
{
document.write('<p align=center><a href="http://www.ferrepress.com/links/campanna.asp?Id=199" target="_blank" rel="NoFollow"><img width="468" height="60" src="/adv/imcoinsa/ban_imcoimsa.gif" border="0" alt="Imcoinsa"></a></p>');
}
<!-- AQUA
if(rn3>=33 && rn3<66) 
{
document.write('<object classid="clsid:D27CDB6E-AE6D-11cf-96B8-444553540000" codebase="http://download.macromedia.com/pub/shockwave/cabs/flash/swflash.cab#version=7,0,19,0" width="468" height="60"><param name="movie" value="/adv/aqua/banner.swf"><param name="quality" value="high"><embed src="/adv/aqua/banner.swf" quality="high" pluginspage="http://www.macromedia.com/go/getflashplayer" type="application/x-shockwave-flash" width="468" height="60" alt="AQUA"></embed></object>');
}
<!-- FERROFORMA BEC
if(rn3>=-1 && rn3<-1) 
{
document.write('<p align="center"><a href="/links/campanna.asp?Id=590" target="_blank" rel="NoFollow"><img src="/adv/sika/sika_468x60.gif" align="bottom" width="468" height="60" border="0" hspace="1" alt="FERROFORMA BEC"></a></p>');
}

<!-- Google
if(rn3>=66 && rn3<=100)
{
google_ad_client = "pub-0044876415402739";
google_alternate_color = "FFCC33";
google_ad_width = 468;
google_ad_height = 60;
google_ad_format = "468x60_as";
google_ad_type = "text_image";
google_ad_channel ="1173573978";
google_color_border = "578A24";
google_color_bg = "CCFF99";
google_color_link = "00008B";
google_color_url = "00008B";
google_color_text = "000000";
document.write('<script type="text/javascript" src="http://pagead2.googlesyndication.com/pagead/show_ads.js"></script>');
}