Wii using SD cards?

Wanting to purchase more songs from Rock Band 3 and need a SD card for my Wii. What's the maximum capacity card that the Wii can use? Would like work like an expansion HDD for the Wii, eg: when playing RB3 can I play songs directly from the SD card in my game, or do I have to make space and move something off my Wii and onto the card to put the song directly onto my Wii for it to be played?
Help much appreciated! :D 

Wanting to purchase more songs from Rock Band 3 and need a SD card for my Wii. What's the maximum capacity card that the Wii can use? Would like work like an expansion HDD for the Wii, eg: when playing RB3 can I play songs directly from the SD card in my game, or do I have to make space and move something off my Wii and onto the card to put the song directly onto my Wii for it to be played?
Help much appreciated! :D 

RE4WiiGirl

That's great guys thanks heaps! Does anyone know around how many mbs would the average song be in the RB library? Just so I know how big or small a card i'll need 

Thanks for all your help! I got a 4gb card, which from memory holds over 10,000 blocks, and the average length song on Rock Band is around 150 - 200 blocks! :D