Wii Mod comes with the Mod Pack. Launch that from HBC and see if it will let you mount the hard drive for installing wads. I've never tried it, and my kid's using my Wii right now, so I can't test it for myself.
EDIT: I just tried it. Though it looks like that it tries to do so when you select to mount the USB, it failed for me.
So if you get the same error that I got, you will have to find an SD card to load the .wad files on to install on your system.