Yea I bought the 512 San Disk for like $17 USD. Enough to hold al my songs for Excite Truck. But other than that, I dont need it for pictures. Wat am I gonna do.. take pictures and run to my Wii to see them? hmm, maybe I'll use my Mac. hahaha
If you have a SD slot on your PC or Mac then just insert that sucker and start dragging and dropping mp3 in that SD card. If you dont have a slot or external device to insert SD card then they are really not much money to get at your local electronics store.
Correction, micro SD cards will not work, unless you have the SD adapter for it. But yea, all VC games are stored in your Wii internally. The only reason I have a SD card is for Excite Truck as well. If you have anymore questions please do not hesitate in IMing me.