This has nothing to do with cpanel. This kind of thing would be better asked at the ipb forums that support your forum software.
In the templates of your forums is where you'll add the code for the banner. You should look thru those and try to understand them a bit.
For example using your FAQ button, its an image, and it links to somewhere. Just like you want your banner to do.
The templates somewhere in the header show you the FAQ button code. This is basically the same code you seek.
Code:
<TD>
<A HREF="faq.php?sid=49026ec9e177e9780d00ddc04522add5"><IMG SRC="templates/BBTech/images/BBTech-hd_08.gif" WIDTH=39 HEIGHT=22 BORDER=0 ALT="FAQ"></A></TD>
So to add the banner you'd use that code in the correct area where you want the banner to be placed.
Code:
<TD>
<A HREF="http://www.motoheaven.com/"><IMG SRC="http://img100.imageshack.us/img100/7859/thrustcompanymotoheavenmp5.gif" WIDTH=468 HEIGHT=60 BORDER=0 ALT="motoheaven banner"></A></TD>
I'm not real familiar with the header templates in ipb so where the code is to be placed is anyones guess.
Try the ipb support forums.