[Been Told]

This is a really nice hack!
I needed to modify it very very slightly because I wanted to hide the chatbox from guests.
To achieve that, do this:
After installing the chatbox...

in Navbar find:

<td class="vbmenu_control"><a href="#" onclick="return openChatbox()">Chatbox</a></td>

Replace with:

<if condition="$show['member']"><td class="vbmenu_control"><a href="#" onclick="return openChatbox()">Chatbox</a></td></if>

In FORUMHOME find:

<!-- Chatbox -->
<tbody>
	<tr>
		<td class="thead" colspan="2">
			<a style="float:$stylevar[right]" href="#top" onclick="return toggle_collapse('forumhome_chatbox')"><img id="collapseimg_forumhome_chatbox" src="$stylevar[imgdir_button]/collapse_thead$vbcollapse[collapseimg_forumhome_chatbox].gif" alt="" border="0" /></a>
			<a href="#" onclick="return openChatbox()">$vbphrase[chatbox_chatbox]</a>
		</td>
	</tr>
</tbody>
<tbody id="collapseobj_forumhome_chatbox" style="$vbcollapse[collapseobj_forumhome_chatbox]">
	<tr>
		<td class="alt1" width="100%" colspan="2"><div class="smallfont" align="center"><iframe src="chatbox.php?nofocus=1" width="100%" style="border: 0px" frameborder="0"></iframe></div></td>
	</tr>
</tbody>
<!-- / Chatbox -->

Replace with:

<!-- Chatbox -->
<if condition="$show['member']">
<tbody>
	<tr>
		<td class="thead" colspan="2">
			<a style="float:$stylevar[right]" href="#top" onclick="return toggle_collapse('forumhome_chatbox')"><img id="collapseimg_forumhome_chatbox" src="$stylevar[imgdir_button]/collapse_thead$vbcollapse[collapseimg_forumhome_chatbox].gif" alt="" border="0" /></a>
			<a href="#" onclick="return openChatbox()">$vbphrase[chatbox_chatbox]</a>
		</td>
	</tr>
</tbody>
<tbody id="collapseobj_forumhome_chatbox" style="$vbcollapse[collapseobj_forumhome_chatbox]">
	<tr>
		<td class="alt1" width="100%" colspan="2"><div class="smallfont" align="center"><iframe src="chatbox.php?nofocus=1" width="100%" style="border: 0px" frameborder="0"></iframe></div></td>
	</tr>
</tbody>
</if>
<!-- / Chatbox -->

What it does is, it checks if the person viewing the page has a user ID (i.e. is logged in) and it shows it only to people with a user ID. And since guests have no user ID, it hides the chatbox from the guests.

As I said, a great hack and a very nice alternative for bigger forums!