Just for future reference, there is a search bar to the right column. There you can search for other posts instead of clogging the forums with new ones such as this one.
To add a Wii code you must go to your address book, this is found in the message centre (bottom right of wii main menu), Then you go to create message (bottom left Icon next to calandar), From here you choose address book on the right and then choose register at the bottom!