Authorize.net AIM - Click here to setup an account for Authorize.net account

Payment Provider Name - Enter the name of the payment provider here.

Show As - If you have multiple forms of payment setup, your customers will have a choice as to which method they prefer. Enter the value you would like your customers to see such as "Credit Card", "Paypal" or "Mastercard, Visa" (without the quotes.)

Active - Place a check in the box to make this payment provider active. If this box is not checked, the payment provider will not show up in the payment provider list during checkout.

Demo - If you would like to test the payment provider settings, place a check in the "Demo" box.

Merchant Login ID - Enter your Authorize.net Merchant ID here.

Transaction Key - Enter your transaction key here.

Press the "Submit" button to save your changes.

(The following is from Authorize.net's site)
To obtain a transaction key:

• Log into your Authorize.Net account at: https://secure.authorize.net/
• Click on Settings and Profile in the main menu
• In the Security section, click Obtain Transaction Key
• Enter your Secret Answer (the answer to the Secret Question configured at account setup)
• To disable the old transaction key, click to select Disable Old Transaction Key
  Note: If the Disable Old Transaction Key box is not checked, the old transaction key will automatically expire and become invalid in 24 hours.
• Click Submit

Important Notes

To use Authorize.net's AIM method your site must have an ssl certificate. To enter your path to SSL please visit the "Main Settings" portion of this user manual.

Next you will need to open your layout.tpl.php template file. If you are using the default template set, this is found in templates/default/layout.tpl.php.

Once you open that file remove the following line:
<base href="{$smarty.const.URL}/" />