Seems game site Destructoid has conducted a little experiment on their Wii's grasp of external memory and what they've come up with is that just about any old cheap hard-drive can be used with the Wii!

1- Download the latest firmware on your Wii

2- Format the USB hard Drive to FAT32, maximum 120GB (Though some website claims that a 300GB hard drive works too)

3- Remove Any SD card form the SD slot The Wii should detect your USB hard drive as an SD card. Beautiful!

Sounds great! Although, no games really need one at the moment and I even if they did, I couldn't find a Wii to play them on. Sad Face.

Check out Destructoid's report here HERE