var is_there = false;

if (document.getElementById('zabak_hoarding_2001')) is_there = true;
htmlkod='<iframe style="width: 125px; height: 125px; border: 0;" id="zabak_hoarding_2001" src="http://ad.klik.cz/ad2.php?hoa=2001&amp;trg=0" marginheight="0" marginwidth="0" frameborder="0" scrolling="no"><\/ifr'+'ame>';

htmlkod=htmlkod.toString();
if (is_there == false) document.write(htmlkod);