When you edit a geocache listing there is a check box for using html on your listing. To get there open your geocache listing. On the right side you have admin tools and can click edit.
Make sure the box for "The descriptions are in html" is checked.
Add the following HTML to the bottom of your cache discription to display the logo.
</br><center><a href="http://www.geocachersofne.com"><img src="http://geocachersofne.com/logo/support_logo.jpg" alt="Support Gone" style="width:200px;height:204px;" /></a></center>