Hello,
USB keys do not work well with wii, in general. Get an external hard drive (fat 32 recommend) and everything will be fine.
Often the usb keys give a black screen or do not work at all with the wii.
For your usb key, you can either format it in FAT 32 with ==>
http://www.ridgecrop.demon.co.uk/index.htm?guiformat.htm
or WBFS with the software ==> wbfs manager, and see the result?
But don't expect miracles, with usb keys.
wbfs2fat ==> it is simply used to convert the wbfs format to FAT 32.