[klaattu]

It actually very easy :

In style manager (on the admin cp) open the style you want to put the annoncement box.
Choose the nav bar template (its inside the nav bar breadcrum bla bla part)

with the nav bar template you will see this part .... "almost last part"

____warning this is only how the nav bar looks originally_______

<tr><td class="thead">$vbphrase[miscellaneous]</td></tr>
<if condition="$show['pmstats']"><tr><td class="vbmenu_option"><a href="private.php?$session[sessionurl]">$vbphrase[private_messages]</a></td></tr></if>
<tr><td class="vbmenu_option"><a href="subscription.php?$session[sessionurl]">$vbphrase[subscribed_threads]</a></td></tr>
<tr><td class="vbmenu_option"><a href="member.php?$session[sessionurl]u=$bbuserinfo[userid]">$vbphrase[my_profile]</a></td></tr>
<if condition="$show['wollink']"><tr><td class="vbmenu_option"><a href="online.php?$session[sessionurl]">$vbphrase[whos_online]</a></td></tr></if>

</table>
</div>
<!-- / user cp tools menu -->
</if>
<!-- / NAVBAR POPUP MENUS -->
</if>

after the last </if> insert the following:

<table align="center" border="0" cellpadding="$stylevar[cellpadding]" cellspacing="$stylevar[cellspacing]" class="tborder" width="100%">
<tr>
<td class="tcat"><span class="smallfont"><strong>$vba_options[portal_blockbullet] Anuncios</strong></span></td>
</tr>
<tr>
<td class="$getbgrow" width="100%">

<center><a href="http://www.auto-mania.com.mx/foro/upload"><img src="http://www.auto-mania.com.mx/extras/anuncio.jpg" alt="Haz click aqui para ir al foro" border="1"></a></center>
</td>
</tr>
</table>
<br />

some explanations:

if you change the part that says "Anuncios" to what ever you like that will be the title of the BOX.

AFTER THIS <td class="$getbgrow" width="100%">

whatever you put there will appear INSIDE the box, in thi scase I put an image (centered) with a link and a little pop up explanation on the link.

dont hesitate to ask if you run into trouble...

after that just save the the navbar and voila...!