1. In confirm.php, open Code View.
2. About line 149 or so, you should see this line:
$AuthNet_required[$nextIndex] = "x_test_request";
$AuthNet_required[$nextIndex] = "TRUE";
3. Change the "TRUE" value to "FALSE"
Also, if you search for "Powerful Product for Simple Problem" you will find many answers to your questions and more. Authorize.net was tough to get going, but Ray definitely helped! Anyway, I think that post was a pretty decent summary of the information used.
Hope that helps!