They come in a certain amount, ex: $15 card gets you 15 songs, and a $35 card gets you alot more.
When you get a gift card he will still have to get his credit card down I am almost positive, and he will have a limit on the songs he can get.
Just go out and buy one the song cards from a local place and you can get the songs with no credit card, just a free membership to napster, thats what I do.