Turn on External Data Provider in your ACP.
Add this to your external page.
<script type="text/javascript" src="/forums/external.php?type=js&lastpost=1&forumid=1,2,3"></script>
<script type="text/javascript">
<!-- Start
for(x = 0; x < 6; x++)
{
document.writeln("<p><a href=\"/forum/showthread.php?t="+threads[x].threadid+"\">"+threads[x].title+"</a> - <span class=\"copytext\"> Posted by "+threads[x].poster+"</span></p>");
}
//-->
</script>
note 1: forumid=1,2,3"> is where you select the forum/s to be shown
note 2: x < 6; x++) the 6 is the number of threads to be shown
HTH ;)