I used Photoshop to meld two images into one so I could show the front and back of my card in the same image. You create a new document, then copy and paste your pictures into it to make a single image. So that it would be viewable in the gallery, I saved it as a JPEG rather than as a PSD (Photoshop document). Don't worry about the message warning you that info might be lost. For images, it's no biggie.
Click
here to see my composite image.
I believe that it is possible to insert HTML code into your gallery description. I added a link in the description of one of my cards that took you to a webpage for more info on the ministry project I made the card for. You could link to your template image one of two ways -- first, you could insert the link into the description of the item itself, and that way anyone who viewed it could just click on the link and get the template image. You could also post to the forums and either link to the gallery image of your template or attach the image file directly to your post. Just be sure that you write dimensions on your template, since a picture might not print out at the proper scale.
Clear as mud?