You don't "install" Bannerbomb. You use it to install stuff, eg Homebrew Channel. But anyway, here's what you do.
Download BannerBomb, and HackMii installer
Rename private folder on SD card to somethin else, e.g. privateold
Copy the private folder from BannerBomb to root of SD card
Copy hackmii installer renamed as boot.elf (or .dol can't remember, whichever extension it has to start with)
Stick SD card in wii
Turn on wii and go to settings>data management>channels>Sd card
A dialog should pop up asking if you want to load from SD, press yes
Select what you want to install in HackMii installer. You need Homebrew Channel for homebrew, I'd recommend installing DVDx and BootMii as well (DVDx allows homebrew to use DVDs and BootMii gives brick protection if installed to boot2)
Also, this should be in homebrew section, now games & general discussion