OK, I'd suggest you to download this demo of Natali Blond. This demo will not "eat" your HD's space, because if you are going to buy this card, you'll get the demo clips anyway.
After that hit Buy her show... Now a window appears asking for your confirmation, do you want to purchase this card for 1 credit (Yes or No).
Take a look which price is up there: 1 credit or 2 credits?
IF it still asking for 2 credits, there has to be a bug and we need WA's skills here to get it properly working, I guess.