The documentation on activating authorizenet is horribly sparse, but authorizenet does indeed work. I made it work just now.

The good news is IT’s EASY!

Here are step by step instructions on how to do it.  (Others are invited to jump in with their comments.)

1)  Make sure your hosting company has  PHP 4.0.2 or later, with cURL extension (with OpenSSL support). If you are not sure, contact your hosting company.  This is essential.

2)  In the VirtueMart control panel, click on List Payment Methods.  Make sure Credit Card is active.

3) Click on Credit Card.  Make sure the cards (Visa, Mastercard, whatever) you have set up with your authorizenet.com account are checkmarked, and the other cards are not checkmarked.

4) Click on Configuration tab.  Type in your authorizenet.com Login ID.  Keep it in Test mode for now. Click “Show/Change the Transaction Key” button.

5) Where it says “Please type in your User Password:” enter your JOOMLA user password that you have previously set up on your site. (NOT the authorizent.com password.)

6)  A box will appear where you enter the Authorizenet’s current transaction key.  In the bottom box re-enter your Joomla user password.  Save the panel.   (***)

7)  Make sure Authorizenet is in TEST mode  by logging into your authorizenet account at authorizenet.com)

8   Go to your store and do  a TEST order.  Use the following TEST credit card to do your authorizenet test. Note: The below card only works in TEST mode and will return an error in live mode.)

5424000000000015 MasterCard.   Use any fake name and use any date after today’s date as the card expiration date.

9) Once the above works, go to authorizenet.com and change your account from TEST to LIVE.  And go into the Virtuemart Credit Card configuration tab and change authorizenet from TEST to LIVE.

10) Then do a test charge with a real card.  You can go back to authorizenet.com and VOID that card charge if you do it before the settlement process takes place.

*** NOTE: You get your transaction key by logging into your authorizenet.com account and creating one under Authorizenet’s Settings and Profile link> Obtain Transaction Key link.

ANOTHER NOTE: Interestingly, the above worked WITHOUT the test site using a secure certificate.  However I strongly suggest you set up a secure certificate for your site.

That’s it!