Open styles/yourstyle/theme/common.css and find:
Code:
   /* Search box

   --------------------------------------------- */

After add:
Code:
   #banner-pos {

     position: relative;

     margin-right: 90px;

     float: right;

   }

Refresh your theme.

Open styles/yourstyle/template/overall_header.html

Find: (this may only be a partial search if you have made changes previously but it is about line 96)
Code:
   <div id="wrap">

     <div class="border-left">

     <div class="border-right">

     <div class="border-top">

     <div class="border-top-left">

     <div class="border-top-right">

       <div class="inside" style="direction: {S_CONTENT_DIRECTION}; ">

         <a id="top" name="top" accesskey="t"></a>

         <div id="page-header">

           <div class="headerbar">

             <div class="inner"><span class="corners-top"><span></span></span>

                 <div id="site-description">

               <a id="logo">{SITE_LOGO_IMG}</a>

              <p style="display: none;"><a href="#start_here">{L_SKIP}</a></p>

             </div>

After add:
Code:
   <div id="banner-pos">

   <img src="/url_image_location/ur_image.gif" alt="" />

   </div>

Refresh your template and imageset.

Note: You can adjust the position of your image relative to the right hand side by playing with the value:
Code:
   margin-right: 90px;
In #banner-pos

If you find the image doesn't sit correctly in the vertical you can add:

[code[/code]
margin-top: 5px;[/code]


Like this:
Code:
   #banner-pos {

     position: relative;

     margin-right: 90px;

     float: right;

     margin-top: 5px;

   }
To #banner-pos

Adjust:
Code:
   margin-top: 5px;
In #banner-pos accordingly

I hope that's clear enough

Original source: Knowledge Base - Add an extra image to the right of site_logo