Hi

There are basically two things to be done.

1)Validate the creditcard number captured using javascript or something
2)Verify that the amount can be transacted by you in realtime from the bank through a payment gateway .


1 you need javascript search on google for this
2 http://www.openecho.com/

I think you also need a credit card reader that can interface with apex i am not sure where you can get one although i dont think its that difficult

regards
Hrishy