FYI: If your going to use a prepaid card for purchasing games make sure that it can be used on "International" webs sites like GOG. I don't see this as a problem with GOG, rather a problem with the companies that create prepaid cards and don't make it very clear upfront. Just be aware of this when buying prepaid cards.

UPDATE 10/15: I managed to find a card that does work - American Express Secure Pay Card. I did call the company before hand and was told that yes, purchases had to be in the U.S.. However, I tried the card anyway and it went through without any problems and I checked the American Express web site for the transaction and it did go through - it's listed as "DIGITAL RIVER WORLD PAYMENTS AB - Purchase".

Couldnt you attach the card to paypal, then pay through paypal in your own currency using the prepaid card?

In this case, having called the company that creates this card, I would have to say no. It seems that they are so paranoid in the card being used for "terrorism" and "fraud" that they require personal information, including a U.S. SSN, just to look at the balance of the card. Basically, I got the feeling that if you used the card on the internet via a non-U.S. website or in a way they don't approve of then they have no problem denying the transaction. Not a big deal since the card and the amount put on it wasn't very much. Just a surprise to me as I've never had any issues with any other amex or visa prepaid cards.

Paypal is a US website so it might be worth trying that way, paypal process the payment for you so it is paypal that take the money from your account not gog.

But if they are as paranoid as you say there is a chance that wont work either.

Yeah. And double check besides that, if the country which issues that Pre-paid card, has enforced capital controls or something. Because in that case, even if the card could be used for international payments, now it cannot. Which leaves out the paypal option. But paypal charges even for failed transactions and eats up quite a few bucks for service payment, along other, hidden expenses, not to be displayed anywhere.