Hi Edward,
Adding custom fields to the Confirmation pages is not supported out of the box, however, it's quite possible that you could dynamically add the Membership Start Date and End Date fields using JavaScript added to the Confirm and Confirm Status ascx files based on a value on the page and today's date.
We are also available to add this as a feature enhancement. If you are interested in sponsoring the enhancement, please submit a Quote Request at the following link:
http://www.smith-consulting.com/servi...
Let me know if you have any questions.
Thanks!