I apologize for my poor delivery--don't work well without a script.
Just make sure one of the first things you do, once you have BootMii installed, before you try CIOSs, is to back up your NAND. On the boot menu (boot it with the SD card in) hit the power button to go to the gears (options) and then hit reset to select it. Select the RAM chip --> SD card icon. Save it.
Oh, and don't have any GameCube controllers plugged in at any point until you are done messing with things.
Source tutorial that will get you to where I am: http://gwht.wikidot.com/
Additional coolness to get rid of some annoyances and prevent updates: http://wiibrew.org/wiki/StartPatch