When a form is embedded the submission is protected with SSL. You shouldn't collect credit card information using FormsCentral because the service is not PCI compliant. You should instead use our new integration with PayPal - it supports credit cards and paypal account payments. The credit card info is processed by paypal and they are PCI compliant.
Here is a tutorial on the new payments features: http://forums.adobe.com/docs/DOC-1632