Look into the PayPal.com IPN system.
just encrypting CC information will not be enough, and when you want to bill them again you wont be able to. If you read the .pdf (Manual) with the IPN system on PayPal.com you can do this. Not have to worry about looking after such information.
However if you know a lot about Administration know a lot about E-Commerce and handling CC information than you should be able to store information within a database as long as its encrypted and far far away from hackers to find.
I dont suggest holding them, as you will be liable.