We are also a ProStores Merchant and that's why we have been able to integrate Google Checkout in our store. But you need technical expertise to be able to do the integration. So why not let us do the job and send us an e-mail at
sales@ebunlimited2.com to inquire about services. Note that this is not applicable to all Prostores Merchants. Please refer to the home page as far as the features/limitations of the Integration.