I'm a big fan of MMORPG's, especially Flyff and Habbo Hotel. On Habbo to get Coins I just go to Target and buy the prepaid Coin Cards, so I don't need to give out my credit card or deal with sending checks in the mail. On Flyff I want to buy Gpotato's, but is there a way similar to Habbo where I can buy them without having to give out my address or credit card?

As long as you are doing it directly through their website or a link that THEY give you, then it is safe. Other than that i don't think so.