Take a look at the Hermes IOS 4 thread (yes, it's possible).
Is it possible to use a usb multiport adapter on the Wii? One is used of the HDD and I want to use 2 mics on the other port for the Sing It games for the kids. Thanks!!
I use a cheap non powered 4 port USB Hub and have had no problems with it at all.
Nintendo has said that not all usb hubs are not compatible, but the one in the link that nightstal linked to should work, so some cheap hubs may work and some may not work.
* Nintendo has not licensed any makes of commercially available USB hubs for use with the Wii console. Accordingly, Nintendo cannot guarantee that they will all be compatible with the Wii console. However, without wishing to make any particular recommendation, Nintendo can confirm that it has tested the Premium 4-Port USB hub manufactured by Logitech and that it appears to function properly.