Directory Delight Theme

I have downloaded the 3 column theme, Directory Delight. I like the theme very much. I have widgetized it but I have a question about it. Column 1 hasw Recent Comments, Archives and such. Column 2 has image holders for advertisements and is named Advertisements. Does anyone have any idea how to place ads there? Here is code from advertisement.php:

<div class="125ads">
<a href="#"><img src="<?php bloginfo('stylesheet_directory');?>/images/125x125.jpg" alt="ads" width="125" height="125" /></a>
<a href="#"><img src="<?php bloginfo('stylesheet_directory');?>/images/125x125.jpg" alt="ads" width="125" height="125" /></a>
<a href="#"><img src="<?php bloginfo('stylesheet_directory');?>/images/125x125.jpg" alt="ads" width="125" height="125" /></a>
<a href="#"><img src="<?php bloginfo('stylesheet_directory');?>/images/125x125.jpg" alt="ads" width="125" height="125" /></a>
</div>

[Please post code snippets between backticks or use the code button.]

I tried putting Google aedsense code in but that didn’t work. I appreciate any suggestions.