I have an iTunes gc loaded to my acct but would like to use my credit card as payment instead for a special promo but can't figure out how to chose that as the payment method instead of my iTunes credit popping up
iTunes Store: How to redeem a code - http://support.apple.com/kb/HT1574 - If you have an iTunes Gift Card or other code that you want to redeem in the iTunes Store. Includes hierarchy of how things are charged.
https://discussions.apple.com/message18056833 - Once a gift card is entered it will be charged for any purchases you make until it is used up. Certain things such as gift cards can not be purchased with gift cards and will get charged to the credit card.