This is moving along pretty well. I did indeed making it all the way to https://secure.authorize.net/gateway/transact.dll and see:
The following errors have occurred.
(13) The merchant login ID or password is invalid or the account is inactive.
Is that error code an eCart issue or is something messed up at authorize.net?
Also, if I were to save the customer's information, where is that stored and what kind of file is it creating?