Okay, I have a member page which lists a number of products that active subscribers can add to their order. When they click one of the products, they just click "order" to order and it takes them directly to a payment page. but one of the products I want to be available requires more information to be filled out - a custom field. This custom field already appears on the signup page with this product. How can I make it appear on the member page, only when this product is selected? thanks!
This will require more deeper customization. user's profile will not be updated when user submit renewal form. So you will need to add filed to renewal form in member_add_renew.html template (use jQuery to display or hide it when product selected) then edit member.php and update user's profile if field is being sent.