I don't have a PayPal account, can I pay by Credit Card?

GSi uses PayPal to accept payments, and PayPal offers several payment methods, including all sorts of credit cards. 

Normally, if you have a PayPal account with an active balance, you just log into your account and use your balance for an instant payment. But you also have an option to initiate a credit card or bank account transaction without logging into your account or without creating a new account.

When you are in the payment page, just select the payment method you wish to use.

If you find problems using PayPal, feel free to contact their customer support, they're always helpful and responsive and they surely speak your language.