<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>