While you could capture the details manually, you would need to do that over the phone or a secure page. Email is not secure for the CVV code or other credit card details. Also note that online merchants are forbidden in the USA by Visa from storing the CVV number.
The
PSU stores support "Google Checkout, authorize.net , 2Checkout , PayPal , Paymate , NoChex , WorldPay , PayMeNow , eCheck.net , eWay , eProcessingNetwork , BeanStream , and more." Could you sign up with one of those?
PSU Stores are built using a combination of Joomla! and Virtuemart. More info on Virtuemart:
http://virtuemart.net/