OK... we'd like to test our shopping cart to be sure everything is set up correclty. This may be a silly question, but how should we go about testing each CC we accept? Thanks.

Your merchant banker and your gateway probably gave you test credit card numbers to use.

You should also open a PayPal account. To test that you can must price a bogus product for a buck and get someone you know who has a Paypal account to buy it.