The steps to set up the shopping cart to work with the Authorize.net  AIM method would be:

1. Log into your Authorize.net account at https://secure.authorize.net
   a. Click Settings
   b. In the Transaction Submission section click on the "Password Required" link.
       Click  the "Require Password for ALL Transactions" checkbox to enable it, then click the Submit button.
   c. Click the Settings link to get to the Settings section again. Then scroll to the Transaction Response
       section and verify that your response version is set to 3.1
   d. Scroll down to the Security section and click on the "Obtain Transaction Key" link.
   e. Copy the Transaction Key  (an alphanumeric code)  that will be generated.

2. Log into CartFreak by going to http://username.cartfreak.com/manage
   a. Click on "Users."
   b. Then click on "add user" or edit an existing user.
   c. Then in the "Authorize.net Key" type in the API login ID.
   d. Then in the "Authorize.net Secret Key" field type in the transaction key.
   e. Click "save."
   f. Congrats, you are now finished!

3. Place a test order to make sure it works. Then, if necessary,  log into your authorize.net account and void it.