Show when 1 topic is unread.

[xxx]

I have 1 topic that my members can go to from a banner. (in the forum is the topic hidden).

How can I show at the members when there is a new answer on this topic (just this topic).
I want to show it with a read.gif and unread.gif near my banner.

Who can help???

I have this but i want a picture that says that there is a new reply on the topic.

echo '

<div class="tborder"><table border="0" width="100%" cellspacing="1" cellpadding="4"> ';
echo '
<div class="tborder"><table border="0" width="100%" cellspacing="1" cellpadding="6">
<tr><td class="windowbg2" width="100%" align="center">
<a href="http://www.xxxforum.be/index.php?topic=2263.0"><img src="http://www.xxxforum.be/kroeg.jpg" border="0" alt="Kroeg"/></a></td>
</tr></div>';       
echo '
</table></div>';

[xxx]

How can I show at the members when there is a new answer on this thread (just this thread).
I want to show it with a read.gif and unread.gif near my banner.

No person who can help??