You find your code that looks like this:
HTML Code:
<if condition="$post['replylink']">
<a href="$post[replylink]" rel="nofollow"><img src="$stylevar[imgdir_button]/<if condition="$post['forwardlink']">reply_small<else />quote</if>.gif" alt="$vbphrase[reply_with_quote]" border="0" /></a>
</if>
<if condition="$show['multiquote_post']">
<a href="$post[replylink]" rel="nofollow" onclick="return false"><img src="$stylevar[imgdir_button]/multiquote_<if condition="$show['multiquote_selected']">on<else />off</if>.gif" alt="$vbphrase[multi_quote_this_message]" border="0" id="mq_$post[postid]" /></a>
And put the condition around it so it looks like this:
HTML Code:
<if condition="$post['postid']!=$thread['firstpostid']">
<if condition="$post['replylink']">
<a href="$post[replylink]" rel="nofollow"><img src="$stylevar[imgdir_button]/<if condition="$post['forwardlink']">reply_small<else />quote</if>.gif" alt="$vbphrase[reply_with_quote]" border="0" /></a>
</if>
<if condition="$show['multiquote_post']">
<a href="$post[replylink]" rel="nofollow" onclick="return false"><img src="$stylevar[imgdir_button]/multiquote_<if condition="$show['multiquote_selected']">on<else />off</if>.gif" alt="$vbphrase[multi_quote_this_message]" border="0" id="mq_$post[postid]" /></a>
</if>
</if>
</if>
But, I will re-emphasize that you need to make sure $thread[firstpostid] is defined first in order for that condition to work.