<script type="text/javascript">   
divWeHave = document.getElementsByTagName('DIV');   
replacement = new Array (   
'Первая замена',   
'вторая',   
'третья и т.д.'   
);   

numer = 0;   

for(i=0;i<divWeHave.length;i++){   
if(divWeHave[i].className == 'forumModer'){   
divWeHave[i].innerHTML = replacement[numer]+divWeHave[i].innerHTML.slice(16);   
numer++;   
}   
}   
</script>