Most pre-paid cards that I'm familiar with normally have either a Visa or Mastercard logo on them, even if they also carry a brand name (I'm guessing thats what the MoneyPak is? Not familiar with that one). If the card has one of these, you should be able to use it as the more common type of credit card without problems.
A second option I think would be to setup a paypal account and use the pre-paid card to credit the paypal system, which works well for supporter subscriptions. Hope this helps and good luck!
edit: Just checked the moneypak website's FAQ and they advertise being able to add money to a paypal account using this card without the need of a bank account, so that may be the easiest solution.
Last edited by dabomby at 2/8/2010 7:34:18 PM