Hi ptran504,
If you would like to add images within the template of an active listings, you can do so by revising the item via the following process:
1) Locate your listing in your Saved Listings folder, make any necessary changes, and save.
2)Check the box next to your updated listing in your Saved Listings folder and click the “Get html” button.
3) Copy the html in the popup box.
4) Locate the item on eBay and click the "Revise Item" button.
5) Click "Edit Description" then click the "Enter your own html" tab.
6) Paste the copied html in place of what's there and save your changes.
I hope this helps=)
-Mike