I tried to purchase some DVD's through Chinadvdwholesaler.com and I too had problems at the checkout.
I emailed the guy but he wasn't very helpful, he said try again after Chinese New Years, as they are very busy and most are away on holiday.
Didn't really answer my questions about having trouble paying with VISA but still.
I think you might need to get your VISA card authenticated or something. There were lots of those advertisments when I went to pay, but mine just got stuck on processing the payment.
Let me know if any of you guys have any success.