You don't need a real card to buy at the iTunes store, unless you want to gift somebody. iTunes card has a code which you will enter online in your iTunes account and you can buy movies, music apps from their virtual store. They don't have a real iTunes store so you don't need a real plastic card to shop there.
I agree with aryka. :) If it helps, here's an article on "How To Use an iTunes Gift Certificate" (same as using a gift card code) http://mp3.about.com/od/itunes/qt/How-To-Use-An-Itunes-Gift-Certificate-Use-Your-Gift-Credit-On-The-Itunes-Store.htm