CIM has two versions.
The first is the Hosted CIM. Using this, you don't have to store any data about your customers payment information because all of that information is provided through a form on the AuthNet site itself.
The second is the API version. Using this you gather all of the customer payment information on your own site, do whatever you want with it at your end (such as storing it locally or even NOT storing it locally), and then you pass that information over to the CIM system to be stored.
In either case, once the customers information is stored on the CIM system, you just need to give AuthNet the payment profile ID number of the payment method the customer wants to pay with, and the AuthNet system pulls that data out of the CIM and uses it for the transaction.
If you are going to store the information on your own server anyway, using CIM is probably a waste of your time. CIM is to store customer data so you dont 'have' to.
:)
WHeis