Hi,
We had the same problem on ArtScans.co.uk when transfering all of the existing images from our own image system, to 4images. Assuming that the image information (name, description, etc) is held in a database somehwere, a simple php script could be used to convert the database.
Although the database structures between ArtScans and your site will be different, we can send you our conversion scripts if you want, so it will give you a general idea that you can build on to convert your exisiting images.
Thanks,
Alan.