Also on line 209 of the plugin, your form action, using the_permalink() doesn’t actually place an action into the markup of the page – I know this wont have any effect on the outcome, but just spotted it.

Basically, it looks like the sql statements you use aren’t quite working properly – I’ve managed to create an entry myself by creating 3 sql queries in phpmyadmin which add entries to the wpsc_purchase_logs, wpsc_submitted_form_data and wpsc_cart_contents tables which then actually displays in the back end correctly.