Knoxximus has posted a guide on how to get the most of out your Nintendo Wii's SD Card storage solution. He's managed to get a full 4GB (Non SHDC) MicroSD card to be used with the Nintendo Wii. While this method only works with non-SHDC cards, one can only hope in the near future Nintendo will address this matter officially.
Source : Tehskeen
How to do it : Here