>As Jordan mentioned, all you can do is basic validation. You'll never get the final response to see if the card is ok or not for the payment as only the bank can allow you that.

You can, however, tell from teh ccno what kindof card it is, and validate that against another field. For example, if your routine determines a ccno is Visa and they specified a Mastercard, you've got problems.

For simple data entry, that would be a worthwhile validation.