New Guide to softmod Wii 4.0-4.2

Bannerbomb is an exploit capable of launching homebrew from the System Menu version 4.2 or below.

NOTE: The original Bannerbomb exploit does not work with System Menu 4.2, it only works with System Menu 4.1 or older. However Bannerbomb v2 has been released and works with System Menu 4.2

The exploit works by using a malformed banner to crash the Wii and run code to load the boot.dol placed in the root of the SD card. It can be used to install the Homebrew Channel, DVDx and the BootMii public beta via the HackMii Installer

for System Menu 4.1 and older
for System Menu 4.2

What you need
SD (or SDHC, only on System Menu 4.0 or higher) card formatted as FAT16 or FAT32.
SD card reader for PC or a PC with one built-in
Bannerbomb channel data on your SD Card
Some homebrew to load (Recommended, HackMii installer) A system menu between 4.0 and 4.2. (System Menu 4.3 prevents Bannerbomb from executing.)
Guide
If your SD card has a private directory with saved channels, rename it temporarily, e.g. to "privateold". Having other saved channels on the same card will screw it up. (You can skip this step if you don't have any channels on the SD card. Saves are fine.)
Copy the Bannerbomb "private" folder to the root of your SD card.
Take your Wii executable, name it "boot.dol" or "boot.elf" if it isn't already, and save it in the root directory of your SD card.
Put your SD card in your Wii and turn it on.
For Bannerbomb v1: Go into Wii Options --> Data Management --> Channels --> SD Card.
For Bannerbomb v2: Go to the SD Card Menu on the main System Menu screen
A message should appear asking to "load boot.dol/.elf". If it freezes or does not appear, download the next .zip file from the Bannerbomb websiteand start over.
The homebrew on your SD card will load. Enjoy!