If you are asking about proworlds site,
T-Shirt Designs then I also would like to know about that. It is a great website, but doesn't have a feature to add the transfer info/stock number so a customer could pick several and not have to write them down on a piece of paper.
I think a non-orderable (probably not a word) shopping cart would be a nice tool and could then be sent via email to the website that directed the customer to art4myshirt so that the transfer can be ordered and produced. JMO
Maybe the website could be "branded" and used along with existing websites, or maybe give the database to use and link to a website so that when changes are made at ProWorld, they would reflect on your own site.