You're lucky that I look at ALL the Gamecube games, and not just the single games that I know, otherwise I'd never have seen your question! I'm sure you meant to put it on the Animal Crossing board, and not the Aquaman: Battle for Atlantis board...

In any case, here are the codes you asked for:

Snowman Wallpaper:

UgsIDXZSiLkvHs (The letter between the s and the D is a capital I as in Iowa and Indiana).
MTS&42rCRMDU6R

Snowman Carpet:

MtcLT#fxnnQbFx
MhuBZTiNsuc4qD

Jingle Wallpaper:

UN9oUOCPfb8UnY
WLMK&uSAtiX%d4

All of these codes are to tell Tom Nook; Remember that the codes are case sensitive and from a very reliable source, so if they seem not to work the first time, check the code very closely and try again! Good luck!