I would put it in the footer next to (or replace) the "smarty, ADOdb, opensource, etc" images.

Go to your AdminCP
      --> Skins
            --> Manage Skins
                  --> click on the "browse"-button behind the skin you use (3th icon)
                        --> click on the "edit"-button behind "footer"

<div align='right'>
<a href='http://sourceforge.net/donate/index.php?group_id=121332'><img src='{$includes}/project-support.jpg'></a> 
<a href=""http://smarty.php.net"><img">http://smarty.php.net"><img src="{$includes}/smarty_icon.gif"></a> 
<a href=""http://adodb.sourceforge.net"><img">http://adodb.sourceforge.net"><img src="{$includes}/adodb.gif"></a> 
<a href=""http://www.opensource.org/docs/definition.php"><img">http://www.opensource.org/docs/definition.php"><img src="{$includes}/open_source_button.png" border="0"></a> 
<a href=""http://microformats.org"><img">http://microformats.org"><img src="{$includes}/mfe_white.png"></a> 
</div> 

This is the code for the images. You can put your code behind the <div align='right'> tag. Maybe you can change right into center, you'll see what's best.

Greetz.

Ow yeah, forgot to tell, by placing the code there it will be available on every page on your forum

Greetz.