istock-like program

[login to view URL] ([login to view URL]) - This is an [login to view URL] type site where people buy credits and purchase comic books to download. - The website is located at [login to view URL] - This site uses a program called photostock. This is what I need to get done. - This software works fine with purchasing images. People purchase credits, they find an image that they like, they use a credit, they download the image. What I need to happen is that people find the image of a comic book cover, they use a credit, they're redirected where they can download the comic book as either a .pdf or some other format. I'm not sure whether at a later date I want people to be able to read a few pages before spending a credit. - Once this works, I can combine the two databases together (Joomla and Photostock) and use a wrapper to make it all seem like one. I'd love to have a bridge between the two softwares, but think that might be too much work.