title: magento customer creation and guest to be converted to regular customer
body: <p>Im using magento 1.4.1.1 .Im using google checkout for the payment.
  I buy  a product as Checkout as Guest instead of creating an account(logging as guest) .
  I give my email id as thomas@xyz.com in the billing address.Im able to buy the product.
  After few days i again signup as guest sinc ei first logged in as a guest with the given email id customer account ot be created and the previous and latest order need to be assigned to that customer.
  How i can do that ? Is there a plugin for that ?</p>