I've been playing around with this a little more using the XFBML method instead of the IFrame. This allows users to enter a comment that appears on their wall, and it also enters a better description on the wall too, with your forum banner thumbnail. I've attached a screenshot of how it looks on the wall.
You'll need to register your ap, and get an ID to place into the code below.
http://developers.facebook.com/setup/
You can try it out
http://www.caraudiocentral.net/forums
The thing I'm still unsure of is, sometimes I'll go back to a post and where I clicked like before, it's now saying 'be the first' when I know I clicked it earlier. So I'm not sure if FB is doing stuff on their end that is messing it up or what.
Code:
<if condition="$post[postcount] == 1 AND !in_array($GLOBALS[forumid], array(40, 39))">
<p><fb:like></fb:like></p>
<div id="fb-root"></div>
<script>
window.fbAsyncInit = function() {
FB.init({appId: 'yourappID', status: true, cookie: true,
xfbml: true});
};
(function() {
var e = document.createElement('script');
e.type = 'text/javascript';
e.src = document.location.protocol +
'//connect.facebook.net/en_US/all.js';
e.async = true;
document.getElementById('fb-root').appendChild(e);
}());
</script>
</if>