In your confirm page, you'll want to store these to responses from Authorize.net...
"".(AuthNet_Result("Response Reason Text")) .""
"".(AuthNet_Result("Full Response")) .""
It's been awhile since I did this, but I want to say that the "".(AuthNet_Result("Full Response")) ."" will general a number and the FIRST digit will provide you with what you're looking for...
1 = approved
2 = declined
3 = error
4 = under review