Web Design Question

It is simple I am sure, what I need to do is build a similar site to cafepress.com, it is for another type of business somewhat simliar, but they want people to upload text and maybe images and then on the next page it gives an example on it will look on the finished product. If they like it they can then purchase that item. I just can't find a script that allows me to do so. I was hoping someone has seen something out there. Or if any one as an idea how to do this. Thanks.