Integrate mailchimp to existing website pages:

We currently have four pages on our website which collect email addresses and save them as four different groups in Roman cart where we send out html newsletters. We are changing to mail chimp and would like the four email groups to now be forwarded to our mailchimp account.
However, we do not want to use the standard double opt in which is mailchimp's default. We would like the email address to be entered once only.
Also, on our free activities pages only after the email is entered, the user is allowed to play the free activities and we would like to keep this functionality.
These are the four pages.
http://www.teachkidsenglish.com/free-ecards/free-ecards.php
http://www.teachkidsenglish.com/free-activity/free-activities.php
http://www.teachkidsenglish.com/espanol/free-ecards/free-ecards.php
http://www.teachkidsenglish.com/espanol/free-activity/free-activities.php