How do I create an ISO file for submission to createspace?

I have used createspace in the past for selling my small productions. However, they now require me to submit my DVD via an ISO file. I created my movie in Final Cut Pro and used Compressor to make it small enough for my DVD. Then I used DVD Studio Pro 4 to create my DVD. I just need information on how to create the ISO file to submit to createspace. Could anyone help me out? I can provide more information if needed.