Ok, I think perhaps first you should get yourself a good book on html/css, as you will need it if you plan to run an X-Cart store
The O'Reilly books are great, available on amazon.com.
Next, have a look at this thread, which explains how the template editing process works:
http://forum.x-cart.com/showthread.php?t=21529
Essentially what you need to do is find the template with the image, and add the html code for a link, as I posted above.